Activity / fitness monitors are exploding in popularity, but measuring HR isn't a standard feature yet. Where available, it doesn't work perfectly, and of the products that can measure HR, few are actually meant to measure continuously. There seem to be 2 methods: green light and ECG. Hopefully the release of the Apple Watch means they're maturing somewhat. Apple Watch also shows the smartwatch and fitness tracker categories might merge. This post is to focus on those meant to measure continuously, including while sleeping.
Fitbit - Charge HR, Surge. These are designed to continuously measure your HR. The Charge HR is the smaller one with a tiny OLED screen that's more like a fitness band. Charge HR - 5 day battery life, splash water resistance, auto sleep mode. Only smartwatch capability is caller ID. Non-replaceable strap.
Basis - Peak. Watch sized and shaped. 5 ATM water resistance. 4 day battery life.
Apple - Watch. "Continuous" recording every 10 minutes. No sleep tracking. Too big to wear to sleep anyway.
Microsoft - Band. Looks like it's trying to
Jawbone - UP3. They seem to be having manufacturing difficulties.
Mio - Fuse. 7 day battery life (only 11-13 hours with continuous HRM), 3 ATM water resistance, NO SLEEP TRACKING.
Exercise Only / Manual Measurements
LifeTrak - all their models measure ECG heart rate on demand. Some have sleep monitoring. Large black and white LCD screen. Interesting feature is 1-year battery life with a non-rechargeable battery. It only measures heart rate when you ask it to, but the important question is what does it do with the data? Does it store it? How much can it store? Are the times logged as well? Can you export it?
Bluetooth chest strap e.g. Polar H7. The most accurate portable HR measurement method. Needs a smartphone and can't be worn for 24 hours, I think.