Is my heart rate sensor broken?

I have a Banglejs2. I've posted before about my heart rate being measured too low. This seems fixed since a firmware upgrade at some point, I don't remember when.

About a week ago I noticed that the HRM was getting really hot, whenever it measured. Battery life went down drastically.

I've tried older firmware versions, factory resets, data&app deletion but it still gets hot. However, the measured value seems correct. What does that mean?

That's a shame. I'm afraid it looks like a hardware issue. I haven't seen any watches with it here, but someone else on the forum did report an issue a few months ago with theirs after it got some water inside it.

I think what's happened is somehow moisture gets into where the HRM sensor is, and then you end up with corrosion around the LED contacts - it still works but the LED then requires more power to make it light, and that means the HRM gets hot and wastes battery. I imagine with the HRM off you'll probably get reasonable battery life though?

I'd be interested in whether you can see any corrosion/water signs through the HRM window on the back of your watch?

It might be possible to remove the HRM window (it seems to be held on with some kind of silicone), clean up the back of the PCB with some isopropyl alcohol and then re-attach the window, although I did try here just now on a dead Bangle and it would likely to be a bit tricky to do without chipping the edge of the plastic window slightly.

Thanks. The explanation makes sense to me. Although I'm not aware of any water exposure-definitely not swimming or showering–but who knows. I attached a photo, I don't remember what it looked like before. The two windows on the side do look different from the top/bottom ones. The right is dark, the left is a bit darker on one half (not really visible on the photo).

Did you just pry the window open from outside?

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I am having a similar experience. I have had my bangle.js 2 for a little over a week. The heart rate function was working great, but over the last couple days I've had a similar issue to user151014, where the battery life has dropped dramatically and the HRM first became less reliable and now is not working at all. I have factory-reset twice and have tried to troubleshoot as iteratively as possible. Currently, the only non-default apps I have uploaded are Health Tracker and Heart Rate Monitor. At this point, whenever I try to open HRM it gets stuck on "Please wait....1" (I have waited as long as 10 minutes to see if this will clear. It does not.) I am able to download data from Health Tracker, but it does not have any BPM data, only steps and movement.

It is possible the watch has been exposed to water briefly. It's my understanding that while we should not shower with the watch, it does offer some water resistance. I would hope this was not enough to completely ruin the functionality of one of the primary reasons I purchased this watch.

@user151014 thanks for that photo - from what I can see it looks very clean under there though. The difference in what you see in the windows is expected - it definitely doesn't look like there are signs of corrosion or water...

And yes, I just got a scalpel blade under the window from the back (where you took the picture). Having it warm may help to loosen the glue - however if there are no obvious signs of it being corroded I wonder how worthwhile that might be?

@user159227 sorry to hear that - I haven't heard of anything like this happening before (the only 2 times - this and one other - I heard of this happening it was in older watches).

Is the rear of your Bangle getting hot? Do the LEDs on the HRM still flash when it's on? They should turn off when away from your skin but if you put your finger nearby they should turn on.

And have you updated the firmware to 2v24? Because I know some newer watches were shipped with an older firmware that had an issue with increased power draw caused by the GPS (and I guess it's possibly it could affect HRM accuracy), but 2v24 and later should fix that.

And yes, the Bangle does have some water resistance and should be fine for everyday wear and tear. It's more showers, baths, swimming etc where there's prolonged contact with water, especially if there's detergent and/or hot water involved.