Square Wireless Flasher and Sound Receiver works with the Square Wireless Doorbell/Telephone with Flash & Sound Alert System. Flashes a white light when the doorbell transmitter is activated and flashes an off-white light for the videophone transmitter. The light mode can be set to continuous or flashing, the light duration can be set to either 15 or 90 seconds. Wireless LED flasher remote control system works up to 600 feet (200 yards). Easily adjust the frequency code set so a neighbor's unit won't conflict with your system. Does not work without a transmitter (not included, available separately). Requires 3 AA batteries (not included), and a one-year warranty. Measures 5" x 5".