Magicfly Expandable Wireless Doorbell Kit Operating at 1000 ft Range with Over 50 Chimes Doorbell Chime Alert System [2 Remote Button Transmitter & 2 Plugin Receiver], Black 52 (16 chord) elegant melodies Stable Wireless transmitting Range: 200 meters (300 meters at open area); Excellent materials keeps itself from getting higher temperature & interference; Easy installation; convenient; double-side stickers;long lifetime;; It is easy to DIY; Super power-saving mode; Certifications: All products passed CE, FCC, RoHS approval. <span class="a-text-bold">Certifications</span>: All products passed CE, FCC, RoHS approval. <span class="a-text-bold">Package contents:</span><br> <br> 2 x Transmitter<br> 2 x Receivers<br> 2 x 12V23A battery(10g)<br> 4x screws<br> 4x plastic rings<br> 2 x double-side sticker