What kind of strap is it? Just wet the nodes with warm water before you put it on..
It's an old Suunto strap. ANT technology. I do wet the nodes, but I think in freezing temps it just doesn't pick it up very well. Or maybe my heart does actually do erratic things at -15 and below!
Ha ha maybe. Can't say I've tested straps at those temps! Be interesting to see if the gel makes a difference?