Abstract: A battery free door bell includes a power supply unit connected to two limited-voltage wave-filtering circuit units for providing power to interior circuit and exterior circuit. The interior circuit has a steady voltage unit and a first amplifying circuit unit so as to provide a signal to a music IC unit. A second amplifying circuit unit is connected to a speaker. The exterior circuit has a switch unit, a delay circuit and a third amplifying circuit unit. A storage circuit unit is connected to the delay circuit unit. The third amplifying circuit unit continuously activates the music IC unit.