Ving is the brand name of those magnetic-strip key cards used by just about every hotel I've visited in recent years. (The usefulness of this idea will depend heavily on this near-monopoly, since it minimises compatibility issues.)
To unlock your room (at present), you put the card into the "keyhole"
card-reader, and then *slowly* withdraw it. A green light comes on to show you it worked.
Or, more commonly, you withdraw it not quite slowly enough, and a red light comes on to show you it didn't work.
This second scenario is probable in proportion to your pre-existing stress levels at the time.
So, I propose a device which will draw the magstripe out of the reader at a carefully calibrated rate. This device would need some little prongs to align it with the edge of the "keyhole", and a little (battery-powered? ipod-powered?) motor to slide the magstripe in and out.
To this point, it's almost practicable.
To make it sillier, (annoying the hotel management and enabling the jingling idea title above), I suggest that this device should not push your actual Vingcard (TM), but rather, it should push a little thing resembling a rolled-up metal tape measure, whose own magnetic strip would have been pre-written by applying a card-reader to the proper Vingcard.
This would enable the device itself to fit on your keyring (probably), provided you had somewhere else to stow the card reader.