1. Install the battery: Outdoor- is supplied by 4pcs alkaline battery, easy to replace the battery, indoor- is supplied by rechargeable Li-ion battery.2. Long standby time: long standby time for outdoor- up to six months3. Big and adjustable speaker, clear voice, can be used as mobile interphone.1. Long wireless distance up to 200M2. Easily installed with tape on the wall3. Outdoor- pair with indoor- by learning its code, 1 outdoor- can paired with N indoor-bells and no interference each other. mode: AAA dry battery supply voltage: 5 (V)Type: wireless door size:100*60*14.8mmMaterial:ABScolour:grayPackage Contents:2 * Intercom doorbell(1 outdoor- and 1indoor-bells)1 * USB Charging CableOnly the above package content, other products are not included.Note: Light 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.