[] the button and energy is converted into electrical energy. No need to worry about the battery running out of power [Distinguish front and rear doors] different buttons, and the receiver emit different melodies. It is convenient to know which door has visitors [Brilliant Lights] Very eye-catching lights, very suitable for the elderly or deaf-mute people [150 meters open distance] The actual usage distance is suitable for most families [60 melodies]Rich melodies give the family a more beautiful environment [5 levels of volume] You can choose the appropriate volume according to your family's needs. High decibel volume not miss visitors, low decibel volume not disturb family members' rest [Free Pairing] buttons support up to 8, and there are no restrictions on receivers. [IP44 Waterproof]IP44 supports daily water splashing. If it needs to be placed outdoors, we recommend purchasing an additional professional doorbell waterproof cover, which and longer to use. Specification Receiver size: 95 x 65mm Button size: 74 x 40mm Input:50 / 60hz Volume: 0-110DB Melody: 60PCS Notice: 1. The distance is an open distance. In actual use, the distance be shortened due to the increase in obstacles. 2. Although the frequency is 433MHZ, due to the incompatibility of the self-generating program, it cannot be used with other doorbells or other products. Due to different batches, there may be differences in product appearance, color, and printed text, which not affect the use. Plug Type :EU Plug,it applies to Indonesia, Germany, France, Spain, Italy and so on. Voltage: AC100-240V Colour:Black Material:Plastic Package Contents: 2x button 2x receiver Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.