This Passive InfraRed Alarm system (PIR alarm) can switch on a Lamp or Alarm when it detects the heat from an object like moving person. The name PIR (Passive Infrared) is given to the sensor because it receives the infrared rays passively and do not emit any infrared ray. The lamp or alarm remains on few minutes depending on the mono time setting of the PIR Sensor used. Ready to fix PIR Sensors are available with Fresnel lens to increase sensitivity and to filter ambient light. Its range is around 5 meters at 45 degree cone angle.