Feature:1. LONG CALL DISTANCE: The door bell adopts professional chip, and in flat and open areas, the call distance can be up to 1500M, which is convenient and fast.2. WIDER COVERAGE: The wireless door bell adopts 462MHz radio frequency, with wider signal coverage, good wall penetration performance, and smoother calls.3. 3 LEVELS VOLUME: The intercom door bell supports 3 levels volume adjustment, with a maximum volume of no less than 112 decibels, can also be heard by the elderly.4. BUILT IN BATTERY: The internal and external machines have built in 2000mAh rechargeable lithium battery, ensuring long endurance, with a USB cable for charging.5. LESS INTERFERENCE: This door bell has 3 separate channels, can easily avoid interference in the wireless frequency band, and internal machine can communicate with each other.Specification:Item Type: Intercom Door BellPower: 0.5WChannel: A B C 3 ChannelsNumber of Connection: Up to 3 sets without serial numbers, unlimited connection under the same channel numberBattery: 2 x 2000mAh Rechargeable Lithium Battery (built in, 1 battery per host).Package List:1 x Internal Machine1 x Charging Base1 x External Machine1 x External Machine Bracket1 x USB Cable1 x Double Sided Tape1 x Door Bell Sticker5 x Screws3 x Expansion Pipes