Abstract: A burglar alert system using infrared sensor and detector mechanism has been constructed and tested. A special feature of the system is the detection of human motion across the path of the infrared sensor with a relay output that activates an alarm. Its simple operation is powered by a 12 volt DC battery, from which power is drawn mainly when detection is made by the primary sensing device. Effective detection of human motion and its low power consumption are ensured by the passive nature of the sensor component.