So you've lost your eyeglass case. Yes, again. Gets frustrating, doesn't it? Stop wasting time searching for stuff -- build a device that emits signals you can see and hear, so you can find what you're looking for instantly. Attach remote-control car receivers to any items you frequently misplace, and put the cars' transmitters in a control box that can activate the receivers' lights and sound signals. Then when one of the items goes missing, press the corresponding button on the box, and you'll have it back in no time. Or at least until the next time you need it.
(2) ZipZaps micro RC cars with different frequencies (RadioShack #600-0181; $4.87 or salvaged)
(2) 3V rechargeable batteries (SparkFun Electronics #PRT-08818; $4.95)
(2) 24mm coin cell holders (DigiKey #BH2430T-C-ND; $0.95)
(1) Yellow SPST switch (DigiKey #401-1984-ND; $0.99)
(1) Red SPST switch (DigiKey #401-1985-ND; $0.99)
(1) SPST pushbutton (RadioShack #275-617; $2.69)
(1) Container (we used RadioShack #270-1803; $3.69)
And if you want sound
Five amazing, clean technologies that will set us free, in this month's energy-focused issue. Also: how to build a better bomb detector, the robotic toys that are raising your children, a human catapult, the world's smallest arcade, and much more.