I am also looking for something to measure heart rate, and ideally HRV, while being mobile, so unfortunately @op engr setup would not work.
So far I have come across the Polar H7 Heart Rate Sensor, which seems to do the job when paired with an iPhone (in my case I have an Android phone but I have read that someone managed to get it working with Android also by upgrading to 4.3), it also comes in at a reasonable price.
Has anyone experience with this, or has a better strap option?
I was investigating the watch options also but it seems that the Polar watches don't allow you access to the HRV data, unless you buy the very high end watches, while the Garmin watches have a maximum of 8 hours before they need recharging. But there may be one I have missed, as there are so many options out there.