Features: 1.Self-powered Design -- Adopting Faraday's principle of electromagnetic induction, it can convert kinetic energy into electrical energy with a single touch, which is safe and eco-friendly. 2.Adjustable -- There are 5 gears of volume and 36 ringtones for you to choose. 3.Free Combination -- The transmitter and receiver can be paired at will. One transmitter can be paired with multiple receivers. 4.Power Failure Memory --With a smart chip, it can save the previous setting of ringtone after power off. 5.Exquisite Appearance -- With surface matte, curved surface, frosted translucent silicone and sunflower design on the back, all these make the doorbell prettier and provide you a marvelous sight experience. 6.Easy To Operate -- No wiring, no battery required, plug in and play. Simply install it on the wall. Comes with a backplate, it can also be installed on the rough wall.