Key finder

The first generation key finders were sound based, they listened for a clap or a whistle (or a sequence of same) then beeped to the user to find them. Determining what was a clap or a whistle proved difficult, resulting in poor performance and "false alarms" - Unintended alarms plagued users at the worst possible moments. These early key finders were soon discarded.

As electronics became smaller, radio was used to locate the keys which were fitted with a small receiver. A transmitter was used to activate this receiver. These second generation systems work well except for the obvious and amusing problem - what happens when the user lost the transmitter?

The latest third generation key finders no longer require a separate "base" - they are all functionally identical and based on a peer-to-peer system where each can find all the others individually. The user can, for example, use a wallet to find misplaced keys and vice versa, or a cell phone to find a lost TV remote control. In addition, since each has its own transmitter, it can reply by radio as well as beeping and flashing a light to attract attention. The seeking unit can then follow this beacon to find even a buried set of keys.

Key finders have also been found to be useful to the visually challenged as well as those with memory problems or illnesses such as Alzheimer's disease.

References

http://www.uspto.gov Patent# 6,774,787 Electronic locator system and method