Whenever I check my resting heart rate using the Watch's heart rate glance, it does one of two things:
1) I see one low number (which sometimes seems accurate, e.g., ~70).
A couple of seconds later, the heart rate shown on the screen jumps up to 107 or 121. It does this every single time; it either shows the lower number first then jumps, or goes straight to 107, or 121, but it's always the same number-107 or 121.
OR
2) I get a series of wildly fluctuating numbers, which are way too high, e.g., 138, 159, 174, etc. It's usually something random and usually high numbers. Taking my heart rate manually shows the numbers to be way off.
I tried doing an unpair (erase) of the Watch several times. An AppleCare technician attempted to run a diagnostic on the Watch multiple times, but was only able to run a diagnostic on the iPhone (6S Plus). He could not reach the Watch, which only went to the diagnostics' "Waiting" screen one time out of about ten tries.
So Apple shipped out a new watch. Here's the kicker:
I immediately set up the new watch, and after the setup was complete, the exact same thing is occurring.
This issue has also persisted across (the first Watch) being paired with two different iPhones (a 6 Plus and a 6S Plus, both new), so I think that minimizes a physical defect in the phone being an issue. The Watch was of course unpaired and reset in-between phone changes, multiple times.
I am interested, among other things, about the security aspect of this particular problem.
Edit:
I did see the articles about tattoos. I don't have any tattoos or scars. I wear it tight (it was fitted at an Apple Store). Furthermore, I found a new angle on this: with both watches, if I hold the watch in the air (not against skin or anything else), they give these same multiple BPM readings that look simulated. I work in a security-related field and call me paranoid, but I think the Watch has been rooted. I've ruled out two new Watches, two new iPhones, multiple resets (and set up as new), and now myself (and the watch dangling in the air, apparently)
Best Answer
If the watches are different, and the phones are different, then the only thing that appears to remain the same is you.
You don't mention, but have you ruled out the possibility of there being anything about you? For instance, I remember reading that tattoos could prevent the heart monitor obtaining a clear reading, and there was some talk about people with very black skin also having difficulties. Example article here http://www.bbc.co.uk/news/technology-32537030
The other possibility is whether there is something with the tightness with which you wear it?