Card Beeper is a credit card case that cries out in anguish when there is no card inside. Every 20 seconds, you'll hear a beep if you've forgotten to get your card back from a merchant, or if you've been jacked by a pickpocket. There's a money clip on the back, too, so your cash is safe as well. At $26, this anti-theft (and anti-forget) device could pay for itself with just one incident. Well, unless the thief takes the beeper, too.
Credit card case that beeps every twenty seconds : Card Beeper [Seihin-World] Thanks, Akira!