How accurate is the heart rate monitor?

I happened to have a discussion at my Cardiologists office recently, while undergoing a stress test. I asked because I was concerned that my iWatch was highly inaccurate. Apparently the iWatch technology measures perfusion and in a nutshell the technology is deemed highly accurate for a high percentage of the population as long as the person is at rest. It seems that activities where there are a lot of irregular hand movements can affect the readings and perhaps that is why my results deviate wildly a small percentage of the time.

I personally feel that it may be worth changing my band to mitigate my pulse rate deviation. I happen to have a bit of looseness in my preferred band adjustment and tightening it down one notch feels a bit too tight. I'm going to try a band which can be fit more perfectly. I think that may help.

While on the treadmill hooked up to an EKG we compared the pulse against my watch thrice, and the watch was always two to three beats in range. We did notice a small delay in the watch compared to the EKG. That's hardly any sort of reliable test, but it did make me feel more assured about the performance of my watch. Apparently I need to get more fit. 🙂

A more scientific analysis can be found here and seems to add the observation that the device quality plays a large factor in accuracy.

Evaluation of the accuracy and reliability for photoplethysmography based heart rate and beat-to-beat detection during d…

In general I have found the HR reported by the series 3 to be consistent (within 1-2bpm) of more traditional HR counting, when at rest. I get frequent spikes & dips that appear abnormal. So I did an off-ball test. Placing the watch against a black plastic camera cover & placing the watch against a folded over white sheet of paper. Interesting HR's reported against these inanimate objects.

Using the Heart Rate app instructs Apple Watch to measure your heart rate, so it will attempt to do so regardless of the nature of the object that is placed against the back of the watch at that time.

When doing so, it uses photoplethysmography. The watch cannot possibly know that, instead of wearing it, you are holding it against an inanimate object such as a piece of plastic or a piece of paper.

"Testing" it in that way is meaningless.

More information:

Your heart rate. What it means, and where on Apple Watch you’ll find it. - Apple Support

thanks to the crazy readings from my apple watch I now get to see a cardiologist this coming week.
In the meantime I have compared it against other devices. In general, most of the time of those I've compared (mostly at rest), the HR from the watch is within 3-4bpm. The problem is the watch from time to time (usually several times a day) does report values that are often completely different. I've seen differences between 15-35bpm from the watch when I've been able to compare, and usually on each minute interval the watch "corrects" itself and comes back into line, yet between each new minute the watch can go off and give values double or half of where it "should" be.

I read the watch has a range of 30-210bpm, and I can attest to the fact that indeed it does report those values... more often than I would like.
I haven't compared it say to my chest monitor at speed yet, as I'd feel more comfortable doing so under medical supervision.

So my cardio visit was interesting. The bottom line, after ultrasound echocardiogram & treadmill stress test all hooked up, I was told my heart was running perfectly, no problems, and that I should throw away the apple watch as the data its presenting is not reliable & I shouldn't be using what it reports!

Hi

Consumer Reports tested the Apple Watch heart rate sensor against their highest-rated dedicated heart rate monitor and found "no significant differences" between their readings:

http://www.technobuffalo.com/2015/04/27/apple-watch-performs-well-in-consumer-re ports-tests/

Apple has not announced any changes to the sensor for the latest models.

More information:

Your heart rate. What it means, and where on Apple Watch you’ll find it. - Apple Support

https://help.apple.com/watch/#/apdcf2ff54e9