Safety Technology International, Inc. STI-3551 Additional Wireless Entry Alert, Door or Window Transmitter Sensor, STI-3353 Receiver Sold Separately Additional transmitter and magnet to help monitor doors, windows, cabinets or drawers Chime sounds when transmitter and magnet are separated Offers 10 selectable chimes Includes 1 AAA battery UL & CUL Listed, FCC & IC Compliant. Limited one year warranty.