This is an Arduino-based Proximity Sensor circuit wired using the popular HC-SR04 ... If everything goes right,you should see the burning eye of the red LED when there is no object in the safe-zone ...

The ultra sonic circuit is adjusted in such a way as to stay in balance as long the same as the output frequency of the transmitter. If there is some movement in the area covered by the ultrasonic ...

Enclosed are the ultrasonic sensor, a temperature sensor and an LED indicating the power status. On the other side of the CAT5 cable can be found an Arduino compatible board with an XBee shield ...