you should read 'the maffetone method" it is a pretty conservative book on how to train using a HRM. Not sure if you have a medical condtion but you should forget using the HRM during a sprint. I say this because during a sprint , you should just be going hard the whole time.

Just my 2 cents.

I never race with a HRM...Sprints especially. Always felt they were a tool for training, not racing...

Don't use them for any race..
Can't tell ya how many races I've been to from 5k to IM to Ultras and you always run into folks whose HRM is beeping like mad...they are either low,or more often than not, red lining. I know folks who could go alot harder in races but don't because they are more focused on their HRM than the race.
What is the point of using a HRM if you don't pay attention to it?
I think RPE and going by feel is better for race day.
Short races are about cutting lose...(Melville: "If his chest were a cannon he would have shot his heart upon it.")
Longer races are about restraint and pacing and I honestly feel that going by feel on a long race day produces better results.

I try to use an HRM for 1/2 iron and iron. It's basically there to act as a speed limit during the bike leg (usually no need during the run, as my speed is plenty limited there and perceived effort is easier for me to judge on the run).

I used mine for IM and found it helpful

Until you learn about your body and where the HR is relative to the effort, for long races like 1/2s and IMs I would use an HRmonitor. You could blow yourself up easier if not.

Its good to use a HRM if you aren't familiar with the discipline you are doing. For me that is the bike (HIM&IM). It and RPE helps me to judge my pace for the whole race and therefore make more informed decisions about if I should go with that guy or not. I still wear it for the run, but it is more for info than anything else. Note, that it is combined with my RPE as well not just heart rate, I too have a few friends who justy aren't prepared to risk it and therefore never pull a real good result. Heart rate racing for the HIM & IM is the best bet for first timmers or thos who are n ot sure they will make the distance.

However, for short course, I don't wear one because making a mistake in effort won't be as devastating as it is in HIM & IM.

I had a similar experience. When I first got the HRM, I used it in a race but didn't look at it until afterwards and was totally blown away by how high my HR was. I basically had it at 160 for 2.5 hours, and my Z4 starts at 162. But that's what I race at for Olympic or shorter using RPE, so I guess my body knows exactly how to keep it just under anaerobic and can do so for a long time. I was pretty amazed at how well RPE was working for me to keep me exactly at the right place, but also kind of scared by how high my heart rate can go for so long. I know it's okay though because that's how I've always raced and I haven't expired yet :p

I did a duathlon on the weekend and averaged about 175bpm for the entire race (5k/20k/5k). What really surprised me was hitting 191bpm at one point during the first run, given that my max is (in theory) 194bpm.

I felt fine, but I think race nerves/cardiac drift had a lot to do with that. I should probably work on getting that under control before an Ironman.