The Shake-u-lator Calculator ($20) doesn’t require any batteries to operate. Simply give it a quick shake and you’re set to do your algebra. (Update: Link removed because the website closed down.)
This 8 digit display calculator uses Faraday’s Principle of Electromagnetic Energy to operate. You will no longer have to buy replacement batteries for your calculator. This battery-free calculator is powered by shaking the calculator side to side. Shake the calculator so that the magnet slides through the copper coil in the visible chamber around 20-25 times, and enough electricity is generated to operate for 10 minutes. If the digits on the LCD screen dim, just shake it a few more times to recharge – their calculations won’t be lost during recharging…