Expensive locks didn’t help me when my office was robbed a few weeks ago, in broad daylight. The thief who made off with the computers was identified and caught through the vigilance of someone in my building who noted a suspicious character lurking about. This experience points to the importance of natural surveillance for crime prevention, one of the principles of CPTED (Crime Prevention Through Environmental Design). CPTED, an approach that originated in the 1960s, is based on a theory that the proper design and effective use of the built environment can reduce crime and the fear of crime. Research into criminal behavior shows the decision to commit a crime or not is heavily influenced by cues about perceived risk of being caught. CPTED strategies increase a criminal’s perceived risk of detection using three main strategies: Natural surveillance, natural access control and natural territorial reinforcement. Natural surveillance, sometimes called “eyes on the street,” is achieved by designing the placement of physical features, activities and people in ways that provide maximum visibility and foster positive social interaction among legitimate users of private and public space. Potential offenders feel increased scrutiny and limitations on their escape routes. Examples include placing windows in active rooms — such as kitchens, overlooking sidewalks and parking lots — leaving window shades open or using the shortest, least sight-limiting fence appropriate for the situation. Lighting design is an important element of natural surveillance. Poorly placed lights create blind spots for potential observers and miss critical areas. Although some areas need bright lighting, too-bright security lighting creates blinding glare and deep shadows, hindering the view for potential observers. Bright lighting can highlight people as targets. Lower-intensity lighting often requires more fixtures, but is generally much more energy efficient. Natural access control limits the opportunity to commit crimes by establishing a clear difference between public and private space. Some ways it can be achieved include things like planting low, thorny bushes beneath ground level windows to deter people from looking in. In most cases, fencing should not obscure views and should make it easy for neighbors to connect, building a sense of social interaction. The closer the neighbors are, the more they look out for each other. Another key measure of CPTED is territorial reinforcement, which employs such design elements as sidewalks, landscaping and porches to help distinguish between public and private areas and help users exhibit signs of ownership that give “hands off” messages to would-be offenders. Physical design can create or extend a sphere of territorial influence that potential offenders can perceive. For example, low walls, landscape and paving patterns can clearly define the space around a unit entry as belonging to the residents of the unit. Territorial reinforcement measures make the legitimate user feel safe and make the potential offender aware of a substantial risk of getting caught. It creates a sense of ownership, since owners have a vested interest in protecting their space. The sense of owned space creates an environment where “strangers” or “intruders” stand out and are more easily identified. Some ways of achieving this include building design and landscaping that communicate an alert and active presence occupying the space. Placing amenities such as seating in common areas helps to attract larger numbers of desired users. Similarly, scheduling activities in common areas increases positive uses, attracts more people and increases the perception that these areas are controlled. Research also indicates that outdoor residential spaces with more trees are seen as significantly more attractive, safer and more likely to be used than similar spaces without trees. On the other hand, a fortress mentality with measures like putting up heavy-duty cyclone fencing and razor wire actually communicate the absence of a physical presence and suggests lower risk of being detected. Good care and maintenance are also important, as deterioration indicates less concern and control by the intended users of a site and a greater tolerance of disorder. CPTED takes more upfront effort but usually involves lower long-term costs, lower losses due to crime and higher quality of life.