Hardware stores sell dozens of different doorbell models you can install in your home.

­Doorbells are one of those everyday devices we take for granted. On the surface, they couldn't be simpler: You press a button, which completes a circuit, which turns on some sort of noisemaker. In a world full of computers, cars and televisions, that doesn't seem so impressive.

But when you take off the cover and see what's going on, conventional doorbells are one of the coolest machines around, precisely because of their simplicity. Doorbells put the basic principle of electromagnetism to work in remarkable, innovative ways. In this article, we'll look inside some standard doorbells to see how these devices translate electric current into buzzes, rings and chimes.