I did some Googling looking for answers:
Flip the battery for a few seconds to reset it. Tried it didn't help.
New battery, tried that didn't work.
Then I found a post with people complaing about how often the Garmin soft straps go bad. Crap I figured I was going to have to buy a $50 strap.
The Forerunner is ANT+ but the Forerunner 210 documentation is a little vague about if third party ANT+ HR straps will work. The forums weren't much help. Some said yes some said no. That's forums for you.
While looking up HR straps Power Tap's HR strap popped up. Cool I have one of those hanging in the closet. I put the strap on & waited for it to pair. Nope. HMMM
• If Heart symbol
is off, press and hold menu,
and select HR Monitor > On.
• If Heart symbol
is flashing, from the timer
page, press page to view the heart
rate page.
The Forerunner searches for your
heart rate signal for 30 seconds.
Bingo I now have my PowerTap HR strap working with my Forerunner. I saved $50 & Get to use something I already have. Win Win