bracelet from Bionym uses your heartbeat as a password. The Nymi wristband works with an app on a registered smartphone to provide authentication. Bionym says that once you have authenticated, you remain authenticated as long as you do not remove the wristband. The the device costs $79 for pre-order for the first 25,000 people that order it. It will increase to $99 after that. Nymi is scheduled to ship in spring 2014.
This promotional video for Nymi shows people using the bracelet to pay for items and open your car. These are potential uses, but as CNET notes
it is a possible future use of the device and not a current one. Bionym is working with developers on new Nymi apps beyond the security feature. Take a look: