Feature: 1) The doorbell is comprised of a transmitter and a receiver with the same frequency 2) The transmitter can be fixed to the door with dual-sided foam adhesive, screws, etc. 3) Makes sure not to fix it too close to metal articles, and avoid rainwater 4) It will not consume power when it is of inactive state, and battery will last one year (20 times/day) 5) Receivers are available in DC type and AC type 6) Main unit adopts quality music IC, high-quality speaker, and pleasant sound