thank you all for your reply.
this is about convenience and avoid HRM strap.
so far I wasn't able to find reliable and practical solution for Apple iWatch only, without riding with phone.
No, iPhone at a ride, just iWatch.
what bike computer / display do you use?
how do you sync from above system that uses HRM strap into Apple?
For how long iWatch battery works with heartbeatz? that makes iWatch to measure HR and transmit for every heartbeat?