Here's a page from Boys Life Magazine from February, 1953, on building an electric buzzer for code practice. The background was rather dark, and the text a bit fuzzy, but hopefully you can figure it out. The key could also be just a strip of steel that has some spring to it, rather than using a separate spring. The picture seems to show two size D batteries, which will give you three volts. It's not as easy today to find a buzzer designed to operate on 3V as it was half a century ago. Radio Shack sells a few types of buzzers, but they might work better with a 9V battery.



Here is a plan that you might use for the battery holder. You'll have to scale it bigger or smaller depending on the size batteries you'll use. Cut the battery holder from a piece of sheet metal, then fold it up on the solid black lines and roll the tongues around your batteries.

You could also make a blinker with essentially the same circuit. You would just substitute a flashlight bulb for the buzzer.