Key chain

A key chain is probably the single most ubiquitous worn device. It is in some ways an ideal place to locate any small device one needs to carry:

• it is always carried when not at home (thus to any point of purchase)
• it often has tags or identifiers enabling its anonymous return to the user if it is dropped - key return services specialize in doing this, e.g. "War Amps" in Canada
• it is carried in a sturdy pocket suitable for bulky metal items

The Dexit system relies on a key chain device equivalent to a cash card - friendly retailers readers that take small amounts of money from the device.

There are already car locking schemes that rely one the keychain to be in the proximity of the lock to operate. See Lexus for more on this. It is not yeat Bluetooth but who cares about bluetooth with emergence of Near Field Communication, back'ed by Sony, Phillips and Nokia. And we have to wait for User:Juxo/Bluetooth Car a little more.