Access control systems are quite useful when there is a need to control access to security-sensitive areas inside a building or on a property. When this level of security is required for the access point, there is an equal requirement to monitor the security-sensitive area itself for unauthorized access or “intrusions.” How and where the intrusion is monitored by the access control system can be accomplished in several ways.

A wide variety of electronic sensors can protect against intrusion.

Electronic sensors that are used to protect a security-sensitive area range from a basic magnetic door position switch or lock bolt position switch to more sophisticated electronics such as motion detectors and glass break sensors. The level of security desired will determine the sophistication of the electronic security device.

Door or lock position switches are the most commonly used security devices.


The position switch is an integral part of the access-controlled door. Without the position switch, the access-controlled door would not have the capability to detect when the door is forced or propped open. For example, when an access-controlled door with a door position switch is forced open, the access control system senses that the door was opened by a means other than an authorized access granted by the use of a credential reader. Consequently a “door forced open” alarm would be generated and reported to the access control system computer.

Additionally, if a door is opened via granted access but is then propped open or is not closed after a specified period of time, an alarm generates and is reported as a “door open too long” to the access control system.

Protecting the doors with position switches is a common security practice. It is quite likely a person with an intention to breach security of a protected area is aware of this as well. Windows are an attractive, easy way to penetrate an area with protected doors.


With this in mind, there two commonly used types of sensors to detect access through a window opening. The first: a vibration-sensitive sensor detects when a window is “shocked” by the event of breaking the glass. Vibration sensors are prone to false alarms by a variety of disturbances such as window vibration created from lightning sound pressure or heavy vehicle traffic. The second: sensors that acoustically listen for the breaking of glass. The acoustic sensor is tuned to “listen” for the acoustic frequency range of breaking glass. This sensor is also prone to false alarms from lightning sound pressure and even loud car stereos from passing vehicle traffic.

Door or lock position switches and glass break sensors are very useful for protecting the perimeter but are not very effective at protecting the space inside the security-sensitive area, since doors and windows are not necessarily the primary means to access a security-sensitive area. Therefore protecting the space inside the area becomes the final line of defense against intrusion.

Motion sensors are most commonly used because they are inexpensive and monitor movement in a variety of space sizes. A typical motion detector usually uses passive infrared technology to detect movement. Infrared technology fundamentally looks for a heat signature emitted from the human body and detects the heat movement across a detection field. This technology is prone to false alarms by things like air conditioners, heat registers or heat emitted through large windows.

To help prevent false alarms in motion detectors, microwave technology is added as an additional detection layer. Microwave technology uses electromagnetic energy to detect movement of objects across a detection field. A low energy microwave signal is transmitted from a transceiver antenna in the detector. Energy from a moving target in the detection zone is reflected back to the detector. Microwave sensors are not subject to interference from such factors as ambient temperature, ambient noise, dust or light. The combination of both infrared and microwave technology creates an almost infallible security device for protecting interior open space. Infrared and microwave detection technologies are also useful for exterior applications. However, they are subject to strict environmental guidelines. Nonetheless, if the technology is applied correctly it is just as effective as the interior applications.

Video Security

Most recently the technical advancement in security video has effectively combined motion detection and video technology. With the advent of digital video processing and recording, motion detection is an inherent feature set in the digital recording process. In its simplest terms, video motion detection is achieved by digitally scanning each pixel of a camera view for changes in ambient light. Once detection is attained the video recorder can be programmed to automatically start recording, as well as notify the access control system that there is an intrusion in the protected space.

With the constantly growing need for an effective means to protect people and property, intrusion monitoring will continue to be a necessary feature of the access control system.