[1]: https://www.strava.com
[2]: http://www.wahoofitness.com/devices/hr.html
Works with Ant+ or Bluetooth. As accurate as the chest band, but much easier to put on. No CR2032 batteries to deal with.
[1]: https://www.strava.com
[2]: http://www.wahoofitness.com/devices/hr.html