Password requested on Apple Watch at the worst possible time

The most common trigger is water getting trapped between the sensors and your skin. 

• Before you jump in the pool, tighten your watch band by one notch more than usual.
• Keeping it snug ensures the sensors maintain skin contact despite the water, preventing the watch from auto-locking in the first place. 

Elanhui wrote:

i can see that the heart rate reading is not consistent throughout many of the swims but often drops out.

That is a sign that the watch and its sensors are not maintaining adequate contact with the skin. I have seen this on outdoor walks and outdoor bicycle workouts. The way I addressed it was: tighten watch band by one notch for those workouts; AND ... adjust position of the watch band, moving it slightly away from the hand and a small amount further up the wrist/arm, plus rotating it very slightly to better center the watch and its sensors over the middle of the wrist/arm, as I noticed it seemed to not be fully centered but rather facing outwards very slightly, which puts it a bit more on the bone than the middle of the wrist/arm.

When making these adjustments, I think they are unique to each individual, as would be the tightness of the band. Some individuals' anatomy is not a good match to certain watch band designs. I am using the simple rubber sports band that came with the watch. It conforms nicely but some of the pricier band materials might not.

Sometimes I start a workout and notice everything being recorded except pulse (heart rate) is not. I realize I had forgotten to tighten the band before starting. I then tighten by one notch and adjust the position of the watch to properly center it. Then pulse starts being sensed and recorded properly.

I too normally wear the watch one notch looser for comfort. Ordinarily, it senses pulse fine that way but in a workout, with activity and motion, it must be able to shift just enough to not keep good contact, hence the tightening and slight adjustments which work well for me with my rubber band. It may take some experimentation for you to get the optimal setup, especially as you as using it for swimming, which I have never done. That said, when bicycling there are quite a few bumps and jiggles and I can see that if the watch is even a little bit loose, it does move around.

I’ll try punching another notch in the band to try to get it tighter. It is already worn tighter during my swim than normal as wearing it that tight all the time would guarantee inflammation of the skin under it. I’ve already punched one notch in the band beyond what was originally there for swimming. Thank you for the suggestion.

i can see that the heart rate reading is not consistent throughout many of the swims but often drops out.