When I used to run I always used a cheap Polar. From memory when you raise the watch part up to the strap it would cycle between HR, Time, stopwatch etc.
A mate gave me one at the start and I didn't know this for a couple of years and wished I had a way of knowing how long I'd run without stopping it. Once I found that out it was grand.
Don't use one now as I swim instead of running, bad knees!