1byone Wireless Driveway Alert, Infrared Motion Sensor with 1 Plug in Receiver and 1 Sensor
Basically, there are two parts to the Driveway Alert Doorbell System.
The Transmitter contains a passive infrared PIR sensor, which detects the moving heat created by an automobile engine (or any other noticeably hot object moving at sufficient speed). It can send signal to the receiver. The transmitter should be deployed outdoors, where it will have a clear view of the driveway.
The Receiver mounts inside your home (or business, warehouse, shed, aircraft hangar, secret underground submarine docking station-where you need it, really, provided its within range of the outdoor unit). It contains a LED and a speaker to let you know when the outdoor unit detects motion.