... or a ringtone.
The phone would be marginally thicker than whatever phone you start with, enough to hold 2 or 3 keys.
The keys would come blank, so they could be cut at a store, and reinserted back into the device.
When a slider is pushed, the shaft portion of the key extrudes to unlock your door, or push it all the way out to use it freely.
Now my pockets are more free on those summer days of minimal clothing.
A good backup, but don't lose your phone!-- Giblet, Aug 08 2007 You should be able to call your door before you got home and have it opened for you.-- xandram, Aug 08 2007 This is actually a brilliant idea. But might be better as little module you can stick on the back of any phone. A strip of industrial high tack glue would work fine.-- Galbinus_Caeli, Aug 08 2007 IF you wanted to twist locks with your phone, I think it would need to be set in the phone, to a central metal rib.
I did also think of it is a new case for existing phones, faceplate style.
[xandram] keys are physical and feel secure in your hand. Knowing anyone with the right code/protocol/etc can unlock my door without having to be there for the neighbors to see breaking in is scary.-- Giblet, Aug 08 2007 random, halfbakery