Sensors are able to detect rapid changes in the environment, such as a window opening or glass breaking which may indicate an intrusion or breach of security. The information is then sent to an alarm system’s controller which notifies the central monitoring station (if the client uses a monitoring service).

Alarm sensors are available in a variety of types and price ranges. Some detect motion, others sense door and window openings, and some are able to detect glass breaking or the pressure of a footstep on carpeting. Here is information on some of the most commonly used types of sensors.

PIR (Passive Infrared) Motion Detector

Passive infared motion detector sensors are very popular because of their reliability. They detect movement within the range of the sensor and are included in nearly all alarm systems. Based on an established technology, infrared motion detection senses changes in temperature over time using infared energy. The purpose is to detect a rapid increase in human body temperature, a likely indication of an intruder.

Microwave Motion Sensors

Microwave motion sensors relay signals to alarm control panels when they detect motion or movement using microwave energy. The microwave energy completely fills the area of detection, and can penetrate most surfaces except metal. This limitation makes microwave motion sensors less reliable than other types. Microwave motion sensors also can detect motion behind walls, a sensitivity that may contribute to false alarms. The sensors are used effectively to control the opening and closing of automatic doors in large stores.

Ultrasonic Motion Sensors

Ultrasonic motion sensors, which are available in active and passive types, are among the most sensitive of alarm detection systems, and consequently come at higher cost. The active sensors send out ultrasonic sounds beyond the frequency of the human ear, while the passive sensors consist only of receivers that listen for sounds. Both are among the most comprehensive of detection systems.

Sound Detectors (Glass Break Detectors)

Sound detectors, or acoustic detectors, use acoustic signatures to recognize patterns such as breaking glass. One of the most common applications for a sound detector is the glass break detector, which can use sound analysis and/or air pressure to determine if a window is being broken. When installed properly and free of interference from other window devices such as air conditioners, glass break detectors can be an ideal way to protect against burglars entering your home or business through a window.

Magnetic Detectors (Door & Window Contacts)

Magnetic detectors, a very common form of home burglar alarm sensor, are used to detect when windows and doors are opened. When a door or window opens, the magnet triggers a switch that alerts the control panel to the intrusion. Because magnetic sensors are basic, they are very reliable and used on windows and doors in many home alarm systems.