Arduino can help you build it -- perhaps with a dash of MakerBot thrown in for good measure. The latest homebrew project to hit the ol' inbox sounds an alarm whenever you leave a room without a registered item. Doh (named in Homer Simpson's honor, we presume), uses a trio of devices to track items that you usually travel with, like your keys or a cellphone. After you've assembled the rather complex contraption, you affix color-coded RFID tags to your gadgets, before registering them with the Arduino-based host. If you leave the room without all of the items that you've registered as a "grouping," a door handle-mounted display will indicate what's missing by flashing its color and sounding an alarm. If you've forgotten multiple items, the display will cycle through the associated colors. There's also a two-way "buzzing tag" that beeps until it's found, if you wish to add that to your collection. It's not a turnkey solution by any means, but unlike Homer, at least you're not being tasked with preventing nuclear meltdown. And if you're looking for a time-proven alternative, a pen and a pad of stickies should do. Jump past the break for a demo video, banjo-equipped soundtrack and all.