Yesterday I showed you a machine that turns itself off, also known as a "Useless Machine." The version from yesterday is enhanced with lots of fancy audio and other options; the most common "Useless Machine" is just a box with a switch -- you flip the switch, the box opens, and the machine reaches out to turn off the switch, then closes. Simple, and achievable by mere mortals.
After yesterday's post, many of you asked where to buy these things or how to make them. Well, good news! You can buy a kit from Maker Shed for about $35, or from Frivolous Engineering for $55 partly-assembled. Both kits require you to put things together, but either makes a good starting point. Here's a video showing assembly of these kits:
If you're very handy and want to make your own box from scratch (with parts bought from a local hobby/electronics store), this set of videos shows you how it's done, step by step. Yes, there's soldering involved. (And be sure to check the end of the second video to make sure it's the kind of machine you want!)
Finally, there's a set of instructions from Instructables written up by the Frivolous Engineering crew, if none of the above is doing it for you. Fun fact: the Useless Machine was featured on The Colbert Report in 2010.