All you Green Lantern fans delight!
Idea: Embed a smart-chip into a ring
The ring allows you to:
(1) Pass freely into and around building security, even if you are carrying files/ baby, etc. in your arms; drive your car without a forceable ignition switch
(2) Exchange business
card details with a handshake; secret societies can have a secure handshake; record who you met at a party
(3) Shop without cash; travel without tickets
(4) Identify drug allergies to paramedics
(5) Allow lost kids, drunken spouses and dead soldiers to be sent home
(6) Make encrypted phone calls and using your own account with any mobile phone or land line, gathering your personal messages, SMS, email etc, while you do so
(7) Que music to your personal preferences
(*) Never lose your key, security pass, money, etc., etc.
Notes - Bakedness
This idea has been baked (experimentally) as a subdermal implant. Power rings have been invented too. Most of the applications are in use. It's the system that's new, AFAIK.
Notes - Security
Encryption using public keyrings goes without saying. Biometrics are a possible backup (but just enough to confirm identity/ring match, not to risk personal privacy)
Notes - Privacy
Like an internet browser, the features can be tailored to ensure personal privacy, only sharing as much info as you wish
Notes - Kitsch
It's not for everybody.