Happened to look for local bluetooth Home Assistant integration for buttons and it seems like a PITA (at least at time of the posts). An alternative I’ve thought of would be to get a cheap Arduino with BT and use it to send heart rate data from over it’s USB to Home Assistant using the Firmata integration that already exists. That module, I think, has motion sensing built in so that might open up more possibilities although the first one I’ve thought of involves putting it on a treadmill. That might be the cheapest way to do this. Arduino Nano with BT is €17.50, so not much more than an ANT+ stick.