Two Primary Types of Intrusion Detection Systems

• Motion detector alarms are difficult to evade. sensor of broken window on ceiling image by StarJumper from Fotolia.com

  Most home and business security alarms function using two main types of alarm sensor designs. Window and door contact designs are intended to notify the alarm control panel when anyone uses the door, opens a window or breaks a window. Motion detector alarms are intended for use when a building is entirely unoccupied and any movement within the building is a sign of something being wrong. The control panel determines, based upon pre-programmed criteria, which types of events warrant triggering an alarm and sending for outside assistance.

Window and Door Contact Alarms

• Window and door contact alarms operate on a simple design: two electrically active sensors completing a circuit when in physical contact. When the two sensors are moved apart, the circuit is broken and the security control system detects that something has occurred. This type of two-part sensor also works on solid windows that are not intended to be open, because when the window breaks, the half of the sensor attached to the window will fall and therefore trigger the alarm.

Motion Detector Alarms

• Motion detector alarms are best placed at key points within a building where people are likely to gain entry, such as lobbies and reception areas. Motion detector alarms are also placed in rooms with ground-level access and windows which could be broken. There are a few different subtypes within motion detector alarm sensors, but the most common type is infrared temperature sensors. The sensor monitors the overall temperature of the room and when the temperature reading changes, as is the case when a human being enters the room, the alarm link to the sensor is activated. Motion sensor alarms are extremely difficult to bypass.

When to Use Contact and Motion Alarms

• It is possible for a thief to bypass contact sensor alarms through the skillful use of tools; therefore contact sensors should be used in combination with other detection methods such as motion detection -- especially when no human security is present. Contact alarms are useful in situations where multiple entrances and exits need to be monitored by a local security force at a central control room. When monitored by nearby security personnel, individual alarm situations can be investigated immediately in person. Since it is possible to bypass contact sensors, security officer patrols can help offset the deficit in security without necessitating the addition of motion sensors, which are often unsuitable for buildings that see heavy traffic at all hours of the day.