Feature: 1. Long Distance: The intercom door bell adopts professional chip, and in flat and open areas, the intercom distance can reach 2000 meters, which is efficient and convenient. 2. Wider Coverage: The wireless door bell adopts 462MHz radio frequency, with wider signal coverage and excellent wall penetration, and internal devices can communicate with each other. 3. Power Supply: The internal and external machine have built in 1800mAh lithium battery, solar charging, the endurance of the inner machine is 3‑5 days on full power, the endurance of the outer machine is 12 months. 4. 16 Channels: The door bell has 16 separate channel options, can easily avoid interference in the wireless frequency band, ensuring stable comm, convenient and practical. 5. 3 Levels Volume: Supports 3 levels volume adjustment, with a maximum volume of no less than 112 decibels, which can be heard by the elderly, with 30 built in ringtones and multiple tone options. 6. IP44 Protection: The intercom door bell has IP44 protection grade, dustproof and waterproof, and can be installed outdoors with confidence, and is equipped with installation accessories. Specification: ​Item Type: Intercom Door BellPower: 0.5W Channel: 1-16 Channel Intercom Distance: Approx. 2000 meter / 6561.7ft Number of Connection: Up to 16 sets without serial numbers, unlimited connection under the same channel number Battery: 2 x 1800mAh 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