The most basic alarm consists of one or more sensors to detect intruders, and an alerting device to indicate the intrusion. However, a typical premises security alarm employs the following components:
• Premises control unit (PCU), or panel: The "brain" of the system, it reads sensor inputs, tracks arm/disarm status, and signals intrusions. In modern systems, this is typically one or more computer circuit boards inside a metal enclosure, along with a power supply.
• Sensors: Devices which detect intrusions. Sensors may be placed at the perimeter of the protected area, within it, or both. Sensors can detect intruders by a variety of methods, such as monitoring doors and windows for opening, or by monitoring unoccupied interiors for motions, sound, vibration, or other disturbances.
• Alerting devices: These indicate an alarm condition. Most commonly, these are bells, sirens, and/or flashing lights. Alerting devices serve the dual purposes of warning occupants of intrusion, and potentially scaring off burglars.
• Keypads: Small devices, typically wall-mounted, which function as the human-machine interface to the system. In addition to buttons, keypads typically feature indicator lights, a small mulch-character display, or both.
• Interconnections between components. This may consist of direct wiring to the control unit, or wireless links with local power supplies.
• Security devices: Devices to detect thieves such as spotlights, cameras & lasers.