Features: 1.The button supports up to 20PCS, and the receiver supports up to 100pcs. 2.If multiple buttons are paired with one or more receivers in the same system, each button can be set to a different ringtone. 3.Power-off memory function: Plug in the power again after power off, no need to re-select and lock the ringtone. 4.The transmitter without screw chuck design to achieve waterproof and dustproof. 5.The transmitter USE a 23A12V alkaline battery (not include battery). 6.Receiving distance:300 meters in open area. 7.Volume:4 levels 25-85db. 8.Melody:58 pcs. 9.Size:Transmitter:77x46x20mm,Receiver:90x56x20mm. NOTE: The button cannot be placed on an iron door because it will interfere with the signal. If you need to change your music,follow the steps below: 1.First select the music you want to use. 2.Press and hold the receiver's music button and you will hear the receiver emit a "dong" sound ahd flash. 3.Press the transmitter twice and the receiver rings again and the music is successfully matched. Package includes: 1 x Button. 2 x Receiver. 1 x Double sided tape. 1 x Screw