Watch with chest strap. Optical heart rate is nowhere near reliable enough for training IMO.

Great thanks

I think that depends on the optical unit.
I switched from chest straps to a Scosche Rhythm+ a couple of years ago and since I found a good location of the Scosche it's been as good as the chest strap (except for battery life!)

Maybe, I've had a Fitbit and a Fenix 5 and neither comes close. Not too bad for running, but hopeless for cycling or swimming.

Both of those ate wrist based which likely has an impact. My Scosche is very solid when used on the front of the upper arm, just above the bicep. It was far less reliable when I tried upper forearm and wrist.

So do you put your heart rate strap on for the swim or put on in T1?

I put it on from the start

Edit: Do you mean wear it or switch it on?

I wear it throughout. When I switch it on depends on the duration of the event versus battery life. The Scosche Rhythm+ is only good for 7-8hrs. Their new 24 should solve that problem and I might get one if it lives up to the reliability of the Rhythm+. I'll wait to hear some feedback!

OHR is highly dependent on the individual. Luckily for me it works really well and I couldn't be happier. Originally started using a Mio Link with a Garmin 910. Then moved though the 235, 935 and now the 645.

Wahoo ticker with my garmin edge 520 on the bike and garmin forerunner 225 on run.

i find it best not to know my HR during races. knowing my heart rate only gets me thinking about my heart rate which raises my heart and that doesn't really serve any purpose at all. i'll wear my hr strap and maybe look at it later, but if i forget the strap, i don't lose any sleep over it.

Interesting - I find my Fenix 5S to be very reliable and consistent. Granted, I haven't done a side by side comparison, but if my wrist strap is snug enough I don't have any inconsistencies hour over hour or even day to day.

Do Garmin watches have HR zone alerts?

Yes

I also use the Scosche Rhythm+ and really like it. Much more accurate than the optical sensor on my watch and more comfortable than a chest strap.

Garmin 920xt, Garmin HRM-Run chest strap. Strap goes under tri-suit, stays there the whole race. 920xt goes on my wrist, stays there the whole race. I press start in multi-sport mode when I step over the timing mat and jump in the water.

I record HR in all workouts, and monitor it in real-time in most of them. So, I have a very good feel for what it will do in most situations. I don't normally pace a race by HR, I use power for that on the bike. But, last September in a local Oly my power meter crapped out. I switched to using HR and RPE to gage my effort, and didn't miss a beat.

I don’t pay that much attention to my HR during races. I mainly use it in case I see it go really high above my “normal”AND not come down. But more than likely my body is telling me to slow down anyway before that happens. Mainly for full distance and half distance. Sprint and Olympic it’s not too useful.