Most of us probably have an old set of corded phones sitting in a box on a shelf somewhere. Even if you don’t, you can find them super cheap. This fun little project, which is great for doing with kids, turns a pair of those corded phones into a DIY intercom.
As DIY blog Make points out, all the circuitry for processing voice is already in the phones. To connect them, you just need a 9-volt battery and a resistor. Check out the video above and then hit up the full build over at Make.