Motion Detectors by 4VWIN. When movement is detected, the Passive Infrared (PIR) sensor sends a wireless signal to the receiver unit from up to 400 feet away. Using the receiver unit, you can choose to be alerted by a high or low chime. PIR motion sensor can monitor driveways, front doors or porches, alleyways, loading docks, waiting rooms, front offices, even warehouses. Switch receiver from a soft to a loud doorbell tone for general use, or a 90dB siren alert.Box Contains2 PIR Transmitter 1 Receiver 1 Instruction Manual 4 Wall Plugs 4 Screws WarningContains small and pointed parts,please be careful with use and keep out of reach of children.