HRM connectivity - HRM watch and Strap

I've had a Suunto T3 for a couple of years, and usually when the numbers start to get wacky it's a sign that one or both batteries are getting low.  Strap battery usually goes quicker than the watch battery, it seems like.  And the batteries are cheap, so that's usually the first thing I try.

You might also try re-pairing the strap with the watch.  I don't think the procedure is in the owners manual, but you can find it on Suunto's website.  You'll probably have to do this anyway if you change the batteries.

I've had two straps go flat dead on me, luckily both replaced under warrantee.  Recently thought my current strap had gone south as well, watch wouldn't find it at all, but then a couple days later the low battery warning showed up on the watch, and replacing the watch battery & re-pairing fixed it.

Might be a contact issue with the strap as well.  If sweat or saliva on the contact patches doesn't do the job initially, I've had good luck using aloe vera gel (the sunburn relief stuff from the drugstore) as an electrolyte gel.