I just stumbled across an interesting product concept called Nymi. It's essentially a wristband that authenticates you via your unique cardiac rhythm every time you put it on, and you can use it throughout the day to unlock your car, sign into your various devices, and make purchases. Of course, this assumes you live in a world full of stuff that's compatible with the Nymi, but I like the idea anyway.

They've got a neat video you can watch to get a better idea of how they envision its daily usage. If you're an app developer and this has piqued your curiosity at all, they've got an API and some SDKs coming soon so you can build stuff for the Nymi (sign up to be notified of their release here).

The Nymi itself isn't available to the public just yet, but you can pre-order it for $79 right now. That pre-order page contains an FAQ section that might answer more of your questions, if you've got any.