The simplest alarm consists of one or more sensors for detecting intruders and a warning device to indicate the intrusion. However, a typical space security alarm uses the following components:

• The space control unit (PCU), the alarm control panel (ACP) or simply the panel: the “brain” of the system reads the sensor inputs, monitors the status of the arm / disarm and signals inputs. In a modern system, it is usually one or more computer circuit boards inside a metal enclosure, along with a power supply. Many newer systems often use sealed outdoor plastic boxes. Some also have control units built into the keyboard or other human-machine interface.
• Sensors: Devices that detect intrusions. The sensors can be located at the perimeter of the protected area, inside it or both inside and at the perimeter. Sensors can detect intruders through a variety of methods, such as monitoring the opening of doors and windows or by monitoring unoccupied interiors for movement, sound, vibration or other disturbances.
• Warning devices: these indicate an alarm status. Most commonly, these are bells, sirens and/ or flashing lights. The warning devices have the dual purpose of alerting occupants on the intrusion and scaring off potential burglars. These devices can also be used to warn occupants of fire or smoke.
• Keyboards: small devices, usually mounted on the wall, that function as a human-machine interface with the system. In addition to buttons, keyboards usually have indicator lights, a small multi-character display, or both.