The doorbell’s iron core will stay at the ding tone bar for as long as the button is held down and the electromagnet energized. When the button is released, it starts a chain reaction that starts with the opening of the circuit cutting the flow of electric current, deactivating the electromagnet, the spring pulls back the metal piston to its original spot, striking the low dong tone bar, completing the ding-dong melody. For every short press of the video doorbell button, the ding-dong tune can be heard repeatedly. Sophisticated chime units contain more than two tone bars that create the elaborate tones. A mechanical doorbell will ring for as long as the person is turning the knob or moving the lever. In this case the ringing is the sound of a striker hitting the metal chime bell or bar.