Hrm

About how it operates and why.

First, the wrist monitor does "polling" on a schedule or scheme of some sort I haven't quite figured out yet. What this means that it's not on all the time, it turns ON and tests the heart rate at intermittent intervals. The reason for this is because having it on all the time would lead to a very short battery life between charges.

Second, it's possible to "force" the monitor to take a reading by simply turning on the Heart Rate Widget. However this does take a bit of time and the length of that time is almost the same as the time out setting for the widget. If you wait a minute or so and turn on the backlight that will usually extend the ON time for the heart rate widget to a period long enough for the Wrist Monitor to get a lock on the heart rate.

Third, my impression is that the heart rate monitor takes a reading when there is a detectable change in the activity level as measured by the step counter accelerometers and that it also may take readings at some pre-determined interval. So it is not the least bit surprising that the monitor turns off when you remove the watch. If you want to "force" it to take a reading when you put the watch back on all you have to do is turn on the heart rate widget.

Another property of this system that I'm guessing at a bit is what the heart rate monitor does between readings. My impression is that it uses what it has "learned" about your personal response to active movement to estimate your heart rate. For example when I am sitting still and typing at the computer my watch generally indicates a heart rate of 62-64 bpm because I'm not moving enough to trigger the step counter. However if I "force" the HRM it will usually show a heart rate of something like 75 bpm because the excitation factor of working on the computer causes my heart rate to rise. Then if I get up and start moving around the house it will typically spike my heart rate up to as much as 125 bpm because when I am being active for exercising it will usually be at that level or a bit higher. The end result is that the short term accuracy can be a bit flakey when it's doing estimated heart rates. However over a 24 hour period I suspect that the total count will likely be within 5% or better. Basically the high readings seem to average out the low readings over time.

Finally, there are things I do that will cause some rather wild errors in the Wrist Monitors readings. For example I was cutting the grass today on my lawn tractor and all the bouncing involved had my wrist monitor reading way way high. At one point it recorded a heart rate of 175 bpm and I am 100% certain that didn't happen. Quite simply the wrist monitor is NOT perfect by any stretch of the imagination. However I do believe that it is useful and expect that as these systems become more common they will also become more refined and the accuracy will improve. Unfortunately to some extent we are all Beta Testers to some extent acting to move the process along.

Now for a tip on this particular system. That is that the tighter you have the watch attached to your wrist the less prone it will be to unstable readings. Because this system is optically based and any movement relative to your wrist will change the "Optical Background" that it relies on to take a reading. I suspect this is why my readings today when cutting the grass were so abnormally high, because I was wearing it a bit loose on my wrist.

Finally, for my workouts I want accurate data so I put on a chest based Heart Rate Monitor. It's been my experience that if the unit is working properly and you have a clean chest strap you'll get good accurate data. It's also been my experience that these units are vulnerable to Sweat so you need to keep a spare on hand and rinse the chest strap out after every workout. BTW, I just had to go to my spare Chest Monitor because the one I've been using the past 9 months started reading way high. I suspect the cause was that over time some trace of my sweat and it's salts had seeped into the electronics and was effecting the circuits. Just out of curiosity I have it in a bag of rice just to see if drying it out will "cure" of reading high. I also plan on purchasing another spare next week. As for the cost, compared to what I am paying for running shoes these monitors are rather cheap.

I second this opinion.
I think you have a faulty unit also.
I don't wear my watch while sleeping. I leave it on the table.
Whenever I take it from the table in the morning, the green lights come up and I see my HR in the widget when I put it on my wrist.
I guess it's time for you to call customer service and get a replacement.