Doorbell Receiver with Button Smart Wireless Door Bell Welcome Chime with 57 Melodies for Home Security M521 57 Chime Wireless Doorbell Waterproof Wireless Door Alarm Contact Sensor Doorbell Main Features: 1. 57 different music tones optional. 2. Memory function, never lose last set whatever power off. 3. The host can set the fixed doorbell music button. 4. Rugged Waterproof Design. 57 Different Ring Tones The wireless doorbell has 57 melody tones and 4 levels of adjustable volume up to 110db. Memory Function Every time you turn on the doorbell, the music is the same melody as the last time you turned it off, no need to reset the previous settings. IP55 Waterproof Design The rugged construction and waterproof design allow the doorbell to withstand all kinds of harsh weather conditions. Keep Your Children Safe The doorbell receiver can connect the door/window sensor. Alert when your little one open the window or the door. 24/7 Lifeguard for Your Family This business door entry chime alerts when burglar opens door and helps deter break-ins(wireless door alarms activates when magnetic sensor separates) Monitor Every Areas You Care with Wireless Door Chime Each wireless doorbell receiver can pair up to 20 magnetic door alarm sensors and each sensor can add unlimited receivers. Up to 390ft/120m Transmission Range (in open area) The long transmission range ensures you will never miss a visitor, even if you are a few rooms away or on another floor. It is enough to cover every door and window in your house. Different Song Use for Different Mode Easy to Installation Plug and Play design is convenient and quick. s a CR2032 lithium battery that boasts 3-year maximum lifespan Installation Steps: 1. Stick the double-sided tape on the back of the waterproof doorbell transmitter. 2. Install the F15 outdoor waterproof wireless doorbell transmitter in the place you need. 3. Plug the M521 wireless doorbell receiver into main power. Technical Parameters: 1. Working voltage: AC 100-220V 2. Working current: