Alarm Sensor Types

Magnetic Detector

• Magnetic detector alarm systems are the most common alarm sensor types, according to Home Security System Advice. These sensors are magnets used on windows and doors to detect when they are opened. The sensors are fairly cheap because there are no electronics associated with them. Each time a door or window is opened, the magnet triggers a switch to the alarm system control panel. The magnet has a metal switch, called a reed switch, which pulls into a closed position when the door or window is shut. When the door/window gets opened, it breaks the circuit, signaling an alarm.

Microwave Motion Sensor

• Microwave motion sensors detect motion and movement. These sensors emit microwave energy to detect movement like ultrasonic sensors. Microwave energy has special properties to penetrate most surfaces, except metal. This can cause the sensor to detect motion where it is not needed. The beam can penetrate walls and pick up normal motion, setting off an unwanted alarm signal. These sensors are extremely sensitive and are prone to false alarms

Ultrasonic Motion Sensor

• Ultrasonic motion sensors come in two types: active and passive. Active sensors emit ultrasonic sounds that are beyond what one can hear with the human ear. Passive sensors have receivers that listen for sound. These are one of the most expensive sensors and one of the most sensitive sensors available.

Passive Infrared Sensor

• Passive infrared sensors detect motion by sensing a change in heat. These sensors are designed to activate the alarm with rapid changes of heat, such as someone walking into a room. The sensor will not trigger if the person is standing still, because it is looking for a change in temperature. A slow change in temperature will not set the alarm off.

Sound Alarm

• Sound alarm detectors recognize patterns such as breaking glass and signal an alarm. These detectors are good for homes with a lot of windows and are good to use even if the magnetic sensors are in use. This way, if someone throws a rock or breaks the glass without opening a door or window, the alarm will still sound. The sensor uses sound analysis and air pressure to determine whether the window is broken.