This small reliable ultrasonic wave alarm trigger was made for use with car alarms, however it is amazing reliable and sophisticated unit. Size is about 2.3" x 4.8" (excluding adjustable pedestal mount). It has a red LED that activates each time it detects a moving object human or pet. Has adjustable sensitivity control and can detect people up to 19-23 ft away. Operates on 12VDC and has long power/output (3 active leads) that terminates into a 3.5mm stereo plug. The tip is (+), the middle is output and the base of the plug is (-). It is simple to add our G24192 Electronic Alert (not included) and each time the unit detects someone it will sound for a few seconds. Brand new in factory box.