Ding Dong. How does the doorbell work?

In my efforts to help clear things up for the kids visiting the Bruckner residence on Halloween, I took the doorbell off our house. Why you ask? Because it was dead and I didn't want kids freezing to death thinking it had worked. Anyways, it's replaced now and I wanted to know how it works. So I asked Ben, and guess what? He knows: 

Traditionally, there is a small transformer located somewhere in your house that converts the 120VAC down to 24VAC, and that lower voltage is connected to a wire that runs to the front door and is attached to your doorbell button. The other side of the doorbell button is then connected to some sort of audible bell, which is then in turn connected to the other side of the doorbell transformer, completing a circuit.  Normally, the doorbell button is basically an open switch so no current is flowing and nothing is happening.  But when someone presses the doorbell button it closes a switch that completes the circuit and current flows into the bell sounding unit.  I'm not sure what they are usually comprised of, but I would guess some sort of solenoid that strikes one bell when the circuit is activated (ding), and then when the doorbell button is released, a spring pulls the striker back and hits another bell (dong).

An alternative method is to have a small battery powered wireless transmitter inside the doorbell button that communicates to a wireless receiver in side the house that is connected to a speaker. The advantage of this approach is that you don't have to run any wires. The disadvantage is that at some point the batteries die out and then the Chinese food delivery guy just stands outside your door hitting a button that does nothing and then waiting for you to notice that he's there while you starve to death inside.