HC-SR04 ultrasonic module distance measuring transducer sensor, uses sonar to determine distance to an object.
Use method: Supply module with 5V, the output will be 5V while obstacle in range, or 0V if not. The out pin of this module is used as a switching output when anti-theft module, and without the feet when ranging modules.
Note : the module should be inserted in the circuit before been power, which avoid producing high level of misoperation; if not, then power again.