Let yourself know if there's someone at the door with the Swann SWHOM-DRIVEA Driveway Alert Alarm. The Swann SWHOM-DRIVEA Driveway Alert Alarm is composed of a transmitter and a wireless receiver unit. Place the transmitter at the area you want to monitor and the wireless receiver unit in your general location at a maximum distance of 200 feet away. When someone passes by the transmitter, it will create a chiming sound on the wireless receiver unit, alerting you if someone has passed the transmitter's sensor field.