Prolly Polar AXN's. The AXN range provides info specifically suited to climbers.
The yellow bands are on the AXN300 (the lowest in the AXN range). The AXN700 has far better features, so my guess would be that they're AXN700's in an AXN300 case to make them stand out. Good marketting ploy, except almost nobody knows that the AXN range exists.
And it can only be a marketting ploy becasue it's unusual that they're on the riders wrists, not on the spare section of the handle bars where they would certainly be more easily read.