Idea

Keep-Me-Close® is a small device that keeps a lost of personal belongings It warns its owner whenever something is being left behind.

Implementation

Implementation is straightforward. In the very near future many items will contain an RFID chip (and if your personal belongings don't, than they can be easily added). This chip contains a unique identifier. The Keep-Me-Close® contains an RFID reader. Items can be registered by keeping it close to the Keep-Me-CLose®. The device continuously scans its surroundigns to see if all items registered are still there. If not, it sounds an alarm, and shows the item that was left behind on its display.

Thanks to Bruce Schneier's CryptoGram for linking to this story .

This is really the opposite of the Digital Matchmaker : keep informed when something gets out of your reach, instead of when it gets within reach.