Systems Surveillance is the process of monitoring the behavior of people, objects or processes within systems for conformity to expected or desired norms in trusted systems for security or social control. See also, deviation analysis.

"Sur-Veillance" is French for "watching over". Note the all seeing "eye-in-the-sky" in this London Transport poster

Surveillance cameras

Although the word surveillance literally means (in French) "watching over" the term is often used for all forms of observation or monitoring, not just visual observation. Nevertheless, the all-seeing eye-in-the-sky is still a general icon of surveillance.

The word surveillance is commonly used to describe observation from a distance by means of electronic equipment or other technological means, for example:

* eavesdropping

* telephone tapping

* directional microphones

* communications interception

* covert listening devices or 'bugs'

* Minox subminiature cameras

* closed-circuit television

* GPS tracking

* Bait car

* electronic tagging

* CCTV Images

* military reconnaissance

* Reconnaissance aircraft, e.g. Lockheed U-2

* Reconnaissance satellites

* "trusted" computing devices

* Internet and computer surveillance

However, surveillance also includes simple, relatively no- or low-technology methods such as direct observation, observation with binoculars, postal interception, or similar methods.

Surveillance, counter surveillance, inverse surveillance, sousveillance

Surveillance is the art of watching over the activities of persons or groups from a position of higher authority. Surveillance may be covert (without their knowledge) or overt (perhaps with frequent reminders such as "we are watching over you"). Surveillance has been an intrinsic part of human history. Sun Tzu's The Art of War, written 2,500 years ago, discusses how spies should be used against a person's enemies. But modern electronic and computer technology have given surveillance a whole new field of operation. Surveillance can be automated using computers, and people leave extensive records that describe their activities.

Counter surveillance is the practice of avoiding surveillance or making surveillance difficult. Before computer networks, counter surveillance involved avoiding agents and communicating secretly. With recent developments; the Internet, increasing prevelance of electronic security systems, and computer databases, counter surveillance has grown in scope and complexity. Now counter surveillance involves everything from knowing how to delete a file on a computer to avoiding becoming the target of direct advertising agencies.

Inverse surveillance is the practice of reversalism on surveillance, e.g., citizens photographing police, shoppers photographing shopkeepers, and passengers photographing cab drivers who usually have surveillance cameras in their cabs. A well-known example is George Haliday's recording of the Rodney King beating. Inverse surveillance attempts to subvert the Panoptic gaze of surveillance, and often attempts to subvert the secrecy of surveillance through making the inverse surveillance recordings widely available (in contrast to the usually secret or restricted surveillance tapes).

Sousveillance (a term coined by Steve Mann, a professor at the University of Toronto) is inverse surveillance that includes the recording of an activity by a participant in the activity. Recent sousveillance workshops such as Microsoft's Continuous Archival and Recording of Personal Experience are evidence of a growing sousveillance industry including Microsoft (wearable cameras), Nokia, Hewlett Packard ("Casual Capture") and many others.

Clinical Surveillance is the monitoring of events (including, for example, the occurrences of infectious diseases or chronic diseases) with a significant impact on public health. Increasingly, clinical surveillance is being used to inform public policy in allocating health care resources and meeting patient needs. As health care becomes increasingly dependent on information systems and the use of clinical surveillance becomes more widespread, privacy concerns may arise. Patient centeredness is a form of clinical sousveillance in which information is managed with equiveillance and transparency.

Equiveillance is the balance between surveillance and sousveillance. It has been suggested that equiveillance might better preserve the contextual integrity of veillance data.

Impact of surveillance

What are you looking at? — Graffiti by Banksy commenting on the neighbouring surveillance camera in a concrete subway underpass near Hyde Park in London.


What are you looking at? — Graffiti by Banksy commenting on the neighbouring surveillance camera in a concrete subway underpass near Hyde Park in London.

The greatest impact of computer-enabled surveillance is the large number of organisations involved in surveillance operations:

* The state and security services still have the most powerful surveillance systems, because they are enabled under the law. But today levels of state surveillance have increased, and using computers they are now able to draw together many different information sources to produce profiles of persons or groups in society.

* Many large corporations now use various form of 'passive' surveillance. This is primarily a means of monitoring the activities of staff and for controlling public relations. But some large corporations actively use various forms of surveillance to monitor the activities of activists and campaign groups who may impact their operations.

* Many companies trade in information lawfully, buying and selling it from other companies or local government agencies who collect it. This data is usually bought by companies who wish to use it for marketing or advertising purposes.

* Personal information is obtained by many small groups and individuals. Some of this is for harmless purposes, but increasingly sensitive personal information is being obtained for criminal purposes, such as credit card and other types of fraud.

Modern surveillance cannot be totally avoided. However, non-state groups may employ surveillance techniques against an organisation, and some precautions can reduce their success. Some states are also legally limited in how extensively they can conduct general surveillance of people they have no particular reason to suspect.

Note: In all the forms of surveillance mentioned below, the issue of patterns is important. Although in isolation a single piece of communications data seems useless, when collected together with the communications data of other people it can disclose a lot of information about organisational relationships, work patterns, contacts and personal habits. The collection and processing of communications data is largely automated using computers. See also: traffic analysis

Telephones and mobile telephones

The official and unofficial tapping of telephone lines is widespread.

The contracts or licenses by which the state controls telephone companies means that they must provide access for tapping lines to the security services and the police.

For mobile phones the major threat is the collection of communications data. This data not only includes information about the time and duration of the call, but also the geographical location where the call was made from and to whom. This data can be determined generally because the geographic communications cell that the call was made in is stored with the details of the call. But it is also possible to get greater resolution of a persons location by combining information from a number of cells surrounding the persons location.

Mobile phones are, in surveillance terms, a major liability. This liability will only increase as the new third-generation (3G) phones are introduced. This is because the base stations will be located closer together.

Postal services

As more people use faxes and email the significance of the postal system is decreasing (this may not be the case in all countries, certainly the case with international communications, but probably not local). But interception of post is still very important to the security services.

There is no easy way to know your post is being read. The machines used to sort and stamp letters often rip up items anyway, so damage is no certain indicator that your post is being read.

The simplest counter-measure to stop your post being opened is to put sticky tape along each edge and the seams of the envelope, and then sign the tape with an indelible marker. That prevents all but the most expert tampering.

People used to send floppy disks via the post. Today these files can go easily by email. But CDs and DVDs of data are still regularly sent by post. To ensure that this data is not open to reading by anyone, even if it's just wrongly delivered, you should encrypt the data.

Surveillance devices - 'bugs'

Surveillance devices or 'bugs' are not really a communications medium, but they are a device that requires a communications channel. The idea of a 'bug' usually involves a radio transmitter, but there are many other options for carrying a signal; you can send radio frequencies through the main wiring of a building and pick them up outside, you can pick up the transmissions from a cordless phones, and you can pick up the data from poorly configured wireless computer networks or tune in to the radio emissions of a computer monitor.

Bugs come in all shapes and sizes. The original purpose of bugs was to relay sound. Today the miniaturisation of electronics has progressed so far that even TV pictures can be broadcast via bugs that incorporate miniature video cameras (something made popular recently during TV coverage sports events, etc.). The cost of these devices has dramatically fallen.

Computer surveillance

At the very basic level, computers are a surveillance target because large amounts of personal information are stored on them. Anyone who can access or remove a computer can retrieve information. If someone is able to install software on a computer system, they can turn the computer into a surveillance device.

Computers can be tapped by a number of methods, ranging from the installation of physical bugs or surveillance software to the remote interception of the radio transmissions generated by the normal operation of computers.

Spyware, a term coined by computer security expert Steve Gibson, is often used to describe computer surveillance tools that are installed against a user's will. Highspeed internet connections have made computers more vulnerable than ever before.


Photography is becoming more valuable as a means of surveillance. In recent years there has been a significant expansion in the level of stills and video photography carried out at public demonstrations in many countries. At the same time there have been advances in closed circuit television (CCTV) technology and computer image processing that enable digital images taken from cameras to be matched with images stored in a database.

Photographs have long been collected as a form of evidence. But as protest and civil disobedience become an ever greater liability to governments and corporations, images are gathered not only as evidence for prosecution, but also as a source of intelligence information. The collection of photographs and video also has another important function - it scares people.

Closed circuit TV

Closed circuit TV (CCTV) - where the picture is viewed or recorded, but not broadcast - initially developed as a means of security for banks. Today it has developed to the point where it is simple and inexpensive enough to be used in home security systems, and for everyday surveillance.

The widespread use of CCTV by the police and governments has developed over the last 10 years. In the UK, cities and towns across the country have installed large numbers of cameras linked to police authorities. The justification for the growth of CCTV in towns is that it deters crime - although there is still no clear evidence that CCTV reduces crime. The recent growth of CCTV in housing areas also raises serious issues about the extent to which CCTV is being used as a social control measure rather than simply a deterrent to crime.

The development of CCTV in public areas, linked to computer databases of people's pictures and identity, presents a serious risk to civil liberties. Potentially you will not be able to meet anonymously in a public place. You will not be able to drive or walk anonymously around a city. Demonstrations or assemblies in public places could be affected as the state would be able to collate lists of those leading them, taking part, or even just talking with protesters in the street.

Electronic trails

Modern society creates large amounts of transaction data. In the past this data would be documented in paper records and would leave a 'paper trail' but today many of these records are electronic, resulting in an 'electronic trail' that is easily reconstructed through automated means. Every time you use a bank machine, pay by credit card, use a phone card, make a call from home, or otherwise complete a recorded transaction you generate an electronic record. When aggregated and analyzed, this information can identify individual behavior patterns that describe how you live and work.

One way to protect autonomy and individual freedom in a paper-based world is through anonymous transactions, for example by using cash. When transactions are electronic, that anonymity may be lost.

Today, large aggregations of transaction information are assembled by marketing, credit reporting, and other data aggregation companies in order to analyze consumer behavior to determine how companies should manage their marketing or sales strategies, or to assess counterparty "trust" for financial transaction. These data sets are also sold to other companies or to government agencies for additional use.

The availability of large data sets of transaction information facilitates the use of automated surveillance or analysis techniques such as data mining to perform dataveillance.

Data profiling of individuals

Data profiling in this context is the process of assembling information about a particular individual in order to generate a profile -- that is, a picture of their patterns and behavior (compare this use of the term data profiling with that used in statistics or data management where data profiling is the examination of information describing the data or data set itself).

Data profiling is used in security, law enforcement and intelligence operations for a variety of applications - for example, to assess 'trust' for security clearances or to grant authorization relating to a trusted system, or to identify or apprehend suspects or threats. The government is able to access information from third parties -- for example, banks, credit companies or employers, etc. -- by requesting access informally, by compelling access through the use of subpoenas or other procedures, or by purchasing data from commercial data aggregators or data brokers. Under United States v. Miller (1976), data held by third parties is generally not subject to Fouth Amendment warrant requirements. Private companies and private investigators can also generally access or purchase data from these aggregators.

Information relating to any individual transaction is easily available because it is not generally highly valued in isolation, however, when many such transactions are aggregated they can be used to assemble a detailed profile revealing the actions, habits and preferences of the individual.

In the past, much information about individuals has been protected by practical obscurity (a term used by Justice Stevens in his opinion in USDOJ v. Reporters Committee, 1989). Practical obscurity refers to the practical difficulty of aggregating or analyzing a large number of data points in different physical locations. In addition, information was often transient and not easily available after the fact. Further, even where data was available, correlation of paper-based records was a laborious process. Electronic (and particulaly digital) record keeping has undermined this practical obscurity by making data easily available and potentially making aggregation and analysis possible at significantly lower costs.

Thus, as more information becomes available in electronic form -- for example, as public records such birth, court, tax and other records are made available online -- the ability to create very detailed data profiles increases and may raise concerns.


There are instances when we wish to hide our identity — to remain anonymous — for a whole range of reasons. To eliminate this will be a serious erosion of our civil liberties. This is possible as we move towards the development of 'electronic identities. There are two aspects to this:

* the development of systems of credentials — where you carry a card or a document; and

* the development of biometrics — where you are recognised from your unique biological characteristics.

The development of identity systems is being pushed on two fronts:

* The banking industry, who wish to find a more fool-proof system of verifying financial transactions than the possession of a plastic card or the use of a signature;

* Law enforcement, who want a way of identifying individuals easily, even if they have no reason (i.e. evidence) to do so. (See Stop and Search )

One of the simplest forms of identification is the carrying of credentials. Some countries have an identity card system to aid identification. Other documents, such as drivers licenses, library cards, bankers or credit cards are also used to verify identity. The problem with identity based on credentials is that the individual must carry them, and be identifiable, or face a legal penalty. This problem is compounded if the form of the identify card is "machine-readable," usually using an encoded magnetic stripe that corroborates the subject's identifying data. In this case it may create a document trail as it is used to verify transactions, like, for instance, swiping an ID card before entering a night club or bar to confirm age and possibly aid police in case of a criminal incident on the premises.

As a means of combating the problem of people carrying or falsifying credentials, researchers are increasingly looking at biometrics — measuring biological or physical characteristics — as a way to determine identity. One of the oldest forms of biometrics is fingerprints. Every finger of every person (identical twins included) has a unique pattern, and these have been used for many years to help identify suspects in police enquiries. A finger/thumb print can be reduced to a brief numeric description, and such systems are being used in banks and secure areas to verify identity.

A more recent development is DNA fingerprinting, which looks at some of the major markers in the body's DNA to produce a match. However, the match produced is less accurate than ordinary fingerprints because it only identifies people to a certain probability of matching. Further, identical twins have identical DNA, and so are indistinguishable by this method.

Handwriting — primarily your signature — has been used for many years to determine identity. However other characteristics of the individual can also be used to check identity. Voice analysis has been used for some as a means to prove identity, but it is not suited to portable use because of the problems of storing a range of voice prints. But perhaps the two most viable portable systems, because identities can be reduced to a series of numeric data points rather than a detailed image or sound, are:

* Iris recognition. Some banks are now using this method of security. The human iris has a unique pattern that can be reduced to a simple series of numeric descriptions. The iris reader matches the pattern of the iris to one stored and verifies the match.

* Facial recognition. The configuration of the facial features can be used to accurately identify one individual from another. Again, the configuration can be reduced to a short numeric description.

By combining some form of personal identifying feature, with a system of verification it is possible to do everything from buying food to travelling abroad. The important issue is how this information is managed in order to reduce the likelihood of tracking. If you were to combine a particular biometric system with new smart card technology to store the description, that system would be immune from tracking (unless the transaction produced a document/electronic trial). But if the identifying features are stored centrally, and a whole range of systems have access to those descriptions, it is possible that other uses could be made of the data; for example, using high resolution CCTV images with a databases of facial identities in order to identify people at random.

Human operatives and social engineering

The most invasive form of surveillance is the use of human operatives. This takes two forms:

* The use of operatives to infiltrate an organisation; and

* The use of social engineering techniques to obtain information.

In groups dealing with issues that are directly contrary to government policy the issue of infiltration often arises. Also, where groups oppose large corporations, infiltration by agents of the corporation may occur. As well as operatives, the police and security services may put pressure on certain members of an organisation to disclose the information they hold on other members.

Running operatives is very expensive, and for the state the information recovered from operatives can be obtained from less problematic forms of surveillance. If discovered, it can also be a public relations disaster for the government or corporation involved. For these reasons, the use of operatives to infiltrate organisations is not as widespread as many believe. But infiltration is still very likely from other organisations who are motivated to discover and monitor the work of campaign groups. This may be for political or economic motivations. There are also many informal links between large corporations and police or security services, and the trading of information about groups and activists is part of this relationship.

It is not possible to guard against the infiltration of an organisation without damaging the viability or effectiveness of the organisation. Worrying too much about infiltration within the organisation can breed mistrust and bad working relationships within an organisation. Rather like other forms of surveillance, the professional infiltration of operatives into an organisation is difficult to guard against.

Another more likely scenario, especially when dealing with third-party collections agencies or banks seeking debt payment, as well as the media or corporate public relations, is social engineering, also known as "pretexting." This involves the inquiring agent phoning or physically talking to the subject in a way as to make him believe they are someone else, or someone with an innocuous interest in the subject. The inquirer's real, clandestine interest is to obtain some specific information that they believe the subject possesses. This form of information gathering is most often used, on a regular basis, by financial operatives pursuing delinquent debts.

In order to avoid disclosing sensitive information to undesirable third parties, precautions may be taken:

* One should not disclose sensitive information over the telephone or in person to unverified third parties.

* Social engineering may be identified by asking a series of questions to see if the inquirer is aware of facts or future plans that they should not be aware of. In case the inquirer claims to represent a familiar financial institution or other "trusted" organization, one may ask for a number to call back, which may then be verified, either through a phone directory or organization website.

Journalists for well known media organisation can be verified by phoning the editor of that organisation, but freelance or independent journalists should be treated with care - they could be working for anyone.

In case one is member of certain organizations, such as activist groups, a balance between privacy and accessibility is often necessary, especially when running a public campaign. This often requires a security policy for dealing with media and other inquiries.

Personal counter-surveillance

Counter-surveillance is reliant on good information security planning. Protecting information is the first stage of counter-surveillance. But counter surveillance must also be seen as a balancing of opposing objectives.

If you are very good at restricting all information, that state or corporations will have problems monitoring you. However, you are also likely to become more isolated and secretive in the process. Therefore, like information security, counter surveillance requires an effort to protect those activities or information that are sensitive, whilst giving less emphasis to those activities that can be open to all.

Information security is primarily based on protecting equipment with security procedures and barriers. Personal counter-surveillance is based on much the same process, but instead you provide security and barriers around your own personal habits. As humans we are creatures of habit. If we exhibit very predictable habits, this makes monitoring of our activities easier. But if on certain occasions we break our habits, it can also give away the fact that we are doing something at that time which is not part of our everyday work.

The best way to begin thinking about avoiding surveillance is to think about breaking the regular patterns in your life. This masks regular activity, so making it harder to practice routine surveillance. But it also masks the times when you may undertake activities out of the ordinary.

Breaking regular patterns does not mean going to bed at different times, or working different hours everyday. Instead it requires that any activities you wish to avoid being the subject of surveillance are integrated into the other events in your life - but not to the extent that they become predictable. If you change the route you take to work or to shop on a random basis, you make it more difficult to monitor your movements. If you build irregular appointments into activities that might involve surveillance, it creates a background 'noise' in the pattern of your activities that masks any change in your habits.

Securing the information on your computer will help your overall security. If you have a portable computer you are presented with a whole new problem because you move that system outside of your ordinary systems of security and access barriers. Therefore special care should be taken with portable computers:

* The system should be secured with a BIOS password to prevent booting;

* Use encryption of the hard disk, where possible, to prevent access to the contents of the hard disk if it is removed from the machine;

* Ensure that your portable computer has different passwords than those used on your static equipment.

Securing your information is fairly easy. But the main issue you will have to deal with when considering personal surveillance is how to carry out meetings, and networking with people, when you need to discuss sensitive issues.

Primarily, when dealing with sensitive information, avoid generating any kind of documentation or opportunities for surveillance. Think about implementing the following as part of your work:

* Travel -

o If you are travelling to a sensitive meeting take a different route going there and coming back, and if possible do not use the same bus or station when going to or leaving the location you are travelling to. This lessens the likelihood that your destination will be identified.

o If travelling on sensitive business, try to use public transport. Using you own private cars will provide a traceable identity.

o To avoid the CCTV systems in public places move with the crowd; don't rush, don't cut corners, and don't look around for CCTV cameras.

o If you can build in other events/appointments as part of your journey, that will help provide an alternate motive for travelling to that area of a town or city.

o Facial recognition systems work primarily on the configuration of facial features. To work they need to get a good view of the face. Looking at a slight angle towards the ground, and wearing a hat with a brim, helps fool the system.

o If you travel using public transport, roaming tickets are preferable to tickets for a specific journey - they give you more flexibility over the route, and they are more difficult to associate a route travelled with a particular ticket purchase.

o If you have the time available and you can obtain a roaming ticket, build in some extra time to your journey and change trains to make it hard to piece together your journey from CCTV and surveillance sources.

o If travelling in a town, avoid moving through the major shopping areas, or 'controlled environments' such as shopping centres. These have the highest level of CCTV coverage.

o Always assume that public transport vehicles have CCTV installed - travelling during peak hours will help mask your presence.

o To make following you in person or via CCTV more difficult do not wear distinctive clothes or carry distinctive objects - blend in.

o Darkness aids anonymity, but is not a foolproof solution to the latest CCTV cameras which can see in the dark.

* Mobile phones -

o If in doubt, turn it off.

o If travelling to a sensitive location, in an urban area do not use your phone within two or three miles of the location, or in rural areas do not use it within ten or fifteen miles of the location. This will prevent the creation of a trail that associates you with that location on that day.

o If the location you are going to is nowhere near a route you regularly travel, turn off your phone before you start your journey there.

o However, do not always go to places far from your home. A truly random sequence will include clustering. If you are always going locations far from your home, they can be able to back track you to your home or office based on the locations you are avoiding.

o If you desperately need to mask your location, let someone else carry your phone around for the day - but this is only realistic if you take all precautions to prevent generating other document trails whilst you are moving around.

* Payments -

o If you are travelling to a sensitive location, don't pay by credit/debit card or take money from a cash machine.

o If you need to spend cash when travelling to/working around a sensitive location, do not spend the notes taken directly from the cash machine (their sequential numbers may be logged). Keep a supply of notes received as change elsewhere and use those.

o If you need to buy something when travelling to/working around a sensitive location, do not give any loyalty cards or personalised money-off tokens as part of your purchases - they are traceable.

* Communications -

o If you need to make a sensitive phone call that must not be directly associated with you, do so from a public phone box. But beware, if you are associated with the person at the other end of the call, and the content of their calls (rather than just the data) is being monitored, your location at that date and time will be discovered.

o If using public phone boxes, try to use them randomly across an area rather than the ones that are closest to you. Also, try to avoid phone boxes on direct transport routes to your home or place of work.

o If you wish to send something sensitive through the post, wear gloves to prevent creating fingerprints when producing/packing the item, do not lick the envelope or stamps to prevent creating a DNA sample, and post it in a different location to where you normally post your letters (the further the better) using stamps bought on a different day.

o If you print something, use a printer that can not be traced back to you. With Printer steganography it may be possible to find out when, and where a document was printed.

o If you need to send a sensitive fax, use a copy shop/bureau which has a self-service desk.

o If you desperately need to keep in communication, buy a pay-as-you-go mobile phone and only use it for a day or two whilst you are engaged in sensitive work.

* Online -

o Maintain a number of alternate personas on the Internet that give you access to web mail and other services should you ever need to use them.

o If you need to use the Internet, use a public access point, such as a cybercafe, a public library that doesn't require an ID, or a college computer lab that doesn't require an ID. Make sure that you do not access your own Internet services from the cybercafe - use an alternate persona.

o If you need to view material that you do not wish to be associated with as part of the server logs of your Internet service provider, use a cybercafe.

o If you use cybercafes as part of your communications, try not to use the same one.

o If you have a laptop computer, and you wish to mask your location, let someone you trust use it online whilst you are away on sensitive work.

* Meetings -

o When organising a private meeting, if you cannot send details to all involved in ways that will not be intercepted always try to agree on meeting in one location near to the meeting place. You can then direct people to the correct location as they arrive. By keeping the location of a private meeting limited, you lessen the likelihood of the location being surveilled.

o If meeting in the home or building of another person or organisation do not make a phone call from their phone to a number that is identified with you, or from a public phone box near to that building.

o If the people going to a private meeting are likely to have mobile phones, ask them to turn them off before travelling to the meeting place (if all the mobile phones of a groups of people are in the same cell at the same time on the same day, it can be assumed that you have had a meeting).

o If you require a private meeting place, do not keep using the same one. Alternate it as much as possible. Also, if you meet in a public place, pick somewhere with a high level of background noise, and with as many obstacles or partitions around the point where you meet, to prevent your conversations being overheard.

o If you must pay for something whilst having a meeting, use cash. Or, if you cannot, get one person to pay. In this way you will not generate paper trails linking you together.

o Meeting in public spaces, streets, in parks, or on public transport is not a good idea - many of these areas are surveilled by CCTV. But bars, cafes and restaurants tend not have their CCTV systems linked to a central control room, and what CCTV systems are installed are concentrated around the till.

All forms of technical counter surveillance is achieved through the use or implementation of Technical Surveillance Counter Measures or TSCM. These measures apply equally for the worried individual as to the diligent corporation. Corporate Espionage is on the increase, and because of this it is an ever increasing threat in day to day life and business.

Natural surveillance

Natural surveillance is a term used in "Crime Prevention Through Environmental Design" (CPTED) and "Defensible Space" models for crime prevention. These models rely on the ability to influence offender decisions preceding criminal acts. Research into criminal behavior demonstrates that the decision to offend or not to offend is more influenced by cues to the perceived risk of being caught than by cues to reward or ease of entry. Consistent with this research CPTED based strategies emphasise enhancing the perceived risk of detection and apprehension.

Natural surveillance limits the opportunity for crime by taking steps to increase the perception that people can be seen. Natural surveillance occurs by designing the placement of physical features, activities and people in such a way as to maximize visibility and foster positive social interaction. Potential offenders feel increased scrutiny and limitations on their escape routes. Natural surveillance is typically free of cost however its effectiveness to deter crime varies with the individual offender.

Jane Jacobs, North American editor, urban activist, urban planning critic, and author of The Death and Life of Great American Cities (1961), formulated the natural surveillance strategy based on her work in New York's Greenwich Village. Natural surveillance is naturally occurring. As people are moving around an area, they will be able to observe what is going on around them, provided the area is open and well lit. Supporting a diversity of uses within a public space is highly effective. Other ways to promote natural surveillance include low landscaping, street lights, street designs that encourage pedestrian use, removing hiding and lurking places, and placing high risk targets, such as expensive or display items, in plain view of legitimate users, such as near a receptionist or sales clerk.

Included in the design are features that maximize visibility of people, parking areas and building entrances: doors and windows that look out on to streets and parking areas, see-through barriers (glass brick walls, picket fences), pedestrian-friendly sidewalks and streets, and front porches. Designing nighttime lighting is particularly important: uniform high intensity "carpet" lighting of large areas is discouraged, especially where lights glare into (and discourage) observers eyes. In its place is feature lighting that draws the observer's focus to access control points and potential hiding areas. Area lighting is still used, but with shielded and cut-off luminaires to control glare. Light sources are typically placed lower to the ground, at a higher density, and with lower intensity than the lighting it is designed to replace.

Any architectural design that enhances the chance that a potential offender will be, or might be, seen is a form of natural surveillance. Often, it is not just the fact that the offender might be seen that matters. It is that the offender "thinks" they will be seen that can help deter the opportunity for crime.


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