Mobile Move Detection

This Mobile PIR Sensor is very easy to build and the whole cost won't be more than 15 Euros (the siren is excluded)  . Basic parts are the pir sensor, a npn transistor (such as BC337,BC546 or 2n2222) and a relay that will activate the siren. So the whole concept goes like that. When motion is detected the "out" pin of pir sensor goes high which activates the transistor, which in sequence energizes the relay (for bigger loads). The schematic is very clear and easy to be followed. Lastly it is being powered by a 9v battery (that's why it is mobile) but with an ac/dc adapter it can be operated from your power plug but it will lose the mobile benefit.