Many installers also charge monthly monitoring fees, which should be taken into account when you shop for a system. These consist of photo cells or magnetic contacts on doors and windows that sound an alarm when an intruder tries to get inside. Perimeter sensors are mounted on two points, such as the door jamb and the door itself. Photo cell sensors are activated when something passes through a beam of light projected between the two points, while magnetic sensors are activated when contact is broken between the two magnetized points. Heat and motion sensors.
Heat detectors respond to body temperatures.
Motion sensors detect movement. Glass break detectors. These devices recognize the sound of breaking glass. They activate the alarm when they sense breaking glass in a window or door. One or more keypads allow you to turn the system on and off.