When conducting an assessment, and creating a subsequent security plan I work with a “defense in depth” concept. Defense in depth creates areas or zones starting from inside the house or business, and building outward (or from the outside looking in if that is your preference). Each zone has its own security considerations and challenges, and will have a perimeter which must be crossed to get into a lower zone before an intruder can reach their target. Items creating the border of can either be psychological, such as indicators of difficulty, they can be deceptive, such as lack of indicators of valuables, or they can be physical, such as higher security locks, strengthened doors, or locked and shatter resistant windows.

One of the key principles of defense in depth is requiring the potential intruder to spend larger amounts of time entering or working inside the premises, and risking greater exposure and chance of getting caught. An intruder will want to spend as little time as possible breaching the house and then less than 10 to 15 minutes actually inside searching and collecting valuables. The short exposure time makes the criminal feel safer as they are typically faster than a police response to a property crime call. If the thief can spend only a few minutes breaching the house and 10 minutes inside they will probably be gone before law enforcement can arrive. If they have to spend more time than that, there is a better chance that they will move on and attempt to enter someplace else. Realizing time and exposure are a factor, we work to maximize both.

For planning considerations in a residential area, I usually use four zones. Businesses may have less or more, depending on their specific situation and location. The number of zones the planner uses is dependent on how the planner is viewing the situation and what is the most convenient. I tend to order the zones from the interior to the exterior, but in this case we’ll discuss them in the order a potential intruder will encounter them. It should be noted the zones can be called anything you wish. Lacking imaginative labels, I simply use one through four.

Outside of your perimeter Zone Four:

Zone four consists of everything in your neighborhood outside of your actual property line. Within this zone are factors you may or may not be able to control or affect. However, threats in zone four may be effectively controlled by working with your neighbors, your housing association, building managers, other area businesses, or local law enforcement agencies. Other than cooperative efforts of the entire neighborhood, the most one may be able to hope for is monitoring situations and reporting possible criminal activity. Awareness of activity in one’s area may increase security for the entire neighborhood.

This is also the zone where a potential intruder will survey the premises and determine if there are valuables worth taking and if it is safe enough to attempt a break in. Trash with indicators of recent purchases, un-secured mail, and high ticket items such as boats, jet skis, or ATVs will aid the intruder. Indicators of open doors and windows, or heavy cover reducing visibility from the street may increase the likelihood of a crime. Lack of these indicators may make the potential intruder check the next location.

Property line to outer wall: Zone Three

Zone three is the area between the outside property line and the actual envelope of the home or business. This may include the yard, driveway, Parking lots, open areas, and fenced in areas. Specific items and deficiencies within zone three can be directly affected by the owner and either modified, eliminated, or repaired. Security is enhanced in zone three through increased physical security measures and direct observation. In some cases, such as apartments or businesses renting space within a shared building, zone three may be very limited or non-existent. This adds a challenge to planning as the only obstacle between zone four’s uncontrolled area and the potential target is the envelope of the structure itself. Lack of visibility into the structure may help deter the intruder due to not being able to determine if there are easily accessed valuables.

In this zone the intruder’s exposure is at its highest. In the fourth zone, they may be just a passer-by, in the second they are inside and less visible. The third zone is where we want to maximize the intruder’s visibility and time.

Outer wall to inner room: Zone Two

Zone two is the area inside the house between the outer envelope and an inner safe room or bedroom. This is the area where a burglar will find most of your valuables. After the outer envelope of the home or business is breached, the intruder is typically able to move easily from room to room and is hidden from outside observation. Items that cannot be found or easily removed within the 10-15 minute window may be abandoned. The burglar may find things in this area, such as keys, that may not be of immediate use, but may be used on a return burglary. He might also see something a very high-value that he cannot to remove immediately and may come back with proper tools or help to extract the item.

Protection of zone two is typically through alarm systems and securing valuable items in areas that are difficult to find or in security containers which are bolted to floors or walls to prevent easy removal. Other options may include stronger interior locks or hidden areas to increase the time the burglar spends in order to conduct a search. Anything which frustrates the intruder during his activities uses time and keeps him from conducting a thorough and effective search.

Zone two is also important because this is where the family may be during the course of a violent home intrusion, or employees during a robbery. Plans must be in place to move people quickly to a safe area in the case of an intruder forcing their way into the building. This will require creating a plan, and practicing a quick response to the threat.

Inner room: Zone One

Zone one is an inner room inside the home or business which may be hardened against an invasion attempt. Typically the area will be an inner room or office, or the master bedroom. This is not to be confused with a “safe room” which is a hardened structure made for long duration safety. The purpose of the zone one room is to create time, to help protect the people, repel the invader long enough to summon law enforcement, and possibly defend the household if required. This inner room may have a number of small improvements, but is fundamentally a product of the homeowner’s security planning. Some improvements for zone one may incur a substantial, many do not.

Response to the intrusion needs to be a planned addition to the security plan and will be what fits the homeowner and family the best. This may not include a violent response to the intrusion, but must include a means to contact outside help. There is the possibility that, in the case of a burglary, the intruder will have no interest in breaching the door or confronting the homeowner, and will leave when he realizes the family is awake, aware of his presence, and has contacted the police.

These zones, and the factors within them are merely a starting point for planning, and not an all-inclusive list. The planner should feel free to adjust the zones as they fit the specific circumstances, and discard the ones that don’t seem to apply. A zone doesn’t even have to be physical. One could create a “cyber” zone to focus on networking and communication issues. All defense in depth really does is aid our planning efforts by allowing us to focus on smaller areas of similar security concerns. Once we determine our zones, we can begin to address factors within the zone to deter an offender, or increase his exposure and chances of detection.