- The eyes and ears of a home alarm system are the sensors that monitor entry points and interior areas. The typical sensors, generally installed on doors and windows, use two magnets: one magnet is connected to the door or window and the other is connected to the door or window frame. When the door or window is opened, one magnet is removed from the vicinity of the other and the sensor registers that the door or window has been opened. More advanced home alarm systems may also contain vibration sensors to detect when glass has been broken by measuring the vibration of the breakage. Many home alarms also use motion sensors that measure the proximity of a room's walls by emitting infrared beams and measuring the time required for them to bounce back; if a beam comes back sooner than expected, it likely bounced off of a person not normally in the empty room and the sensor registers "motion."
- If sensors are the eyes and ears of a home alarm system, the system's control panel is its brain. When the alarm system is installed, each sensor is registered with the control panel either through wires or wireless radio signals. The control panel also interfaces with keypads and other input devices used by the homeowner to control the alarm system.
- Because all of the sensors in a home alarm system are registered with the control center, the control keeps track of the status of the home and reports activity through keypad displays and other output devices. When activity takes places, such as when a window is opened, the sensors report the activity to the control center and the center registers that the activity has occurred. In managed alarm systems, the control panel also polls the sensors to verify that they are still operational; if a sensor fails to respond, the control center alerts the homeowner of a faulty sensor. If the homeowner activates (or "arms") the alarm system and the control center registers activity in the home, a signal is sent by the control to a siren, strobe light or other audio/visual alarm element.
