I’ve seen a number of these tire pressure management systems pass through the FCC over the past few months.  This one from Aspirit Enterprise, Inc., lets you monitor the pressure of your tires from a keychain.  Not a bad idea, I suppose, as poorly inflated tires can really kill your gas mileage.

One problem with these, however, is that they actually replace the existing valve on your tire.  That means you have to disassemble your tire, which is no trivial task.

Each one of these runs on its own battery as well, so you know changing those batteries every few years is gonna be a pain.