Deeply disappointing experience with the Index Sleep Monitor

Interesting.  My experience with the ISM is completely the opposite.  Similar to you I am deeply in the Garmin ecosystem.  But once I figured out how the ISM works, getting it to sync, etc. has been great.  The ISM reliably reports my sleep information, recovery, etc.

I do agree with you on battery life though.  I think I am getting five, maybe six days?  Not sure if that is because when I take the ISM off and turn the band inside out, I leave the band in a darkened room.  So perhaps the ISM thinks it still needs to work and stays on longer than it should?  I do not know.

But battery issues aside, no complaints here.

I wear a Garmin Epix during the day, power off and wear the Index Sleep Monitor at night.  Some mornings I have no sleep data recorded, some days syncs while I am getting ready for the morning and other times I have to prod it to sync and then only sometimes will there be data recorded.  Until I reached out to support I didn't realize that HR data is still getting recorded and sync but no sleep data.  I thought it being a possible conflict with my Epix but I try to make sure the sync with the band happens before powering up the watch - but in reality it shoud just work.  I don't know why the experience is so unreliable.  With the request of support I have removed and reconnected the device to my app but I don't think that will resolve the issue.  I'm hoping that a software fix will come soon.

Same here and didn't work for me either. I bought it direct, Garmin sent me a replacement sensor to try but that didn't improve things. Eventually took a refund. I'd still like to have one, if there's a v2 which states that it addresses these problems I'd try again. 

Thanks for letting me know. The Index is a lot cheaper than subscription fees, so I was interested. The other question I had was about the sizing; I need a large and my wife would need a small and I didn't want to buy 2. I wondered if we could DIY adjust somehow. 

I don’t use the strap, it’s quite wide and has a ridged plastic buckle which it threads trough back on itself which I find uncomfortable, although better than wearing my Epix 51mm. I use a piece of elasticated tubular support bandage, cut to a width to cover the module, and just tight enough to hold the module in place. It doesn’t take much to hold it. A also wear it on the back of my arm, or round my ankle where I hardly notice it.

The bandage is cheap here it the UK, and available in various sizes to suit so that’s an option.

What you can also do is buy the large strap. When your wife uses it don’t thread it through the buckle, just wrap it round your arm, at the end flip the Velcro connector back on itself to connect it. You doesn’t need it tight so it will hold. Works a treat. This way a large strap will go as small as you like. 

I find the strap to be quite comfortable and once I have it on I do not notice it.  Garmin does sell the strap on its own w/o the ISM hardware.  So you could possibly buy the ISM with the small/medium band, and then buy the large band on its own.  You could then share the hardware between the two bands.

If you do not want to spend the money on a second arm band, there is a YouTube video floating around of a woman who used on of children's socks to create an ISM band.  That might be one avenue for you.

Good luck.

Same.  Last night was the final straw, it completely disconnected from my phone, and then when I re-paired it, it once again didn't record skin temperature.  I did not buy this one thru Garmin (which I usually do but I was impatient and wanted this one sooner so, Amazon), so Garmin won't do anything for me which is kind of a bummer, it's still their device.

This experience shows how important stable performance is in wearable sleep trackers. Even accurate data loses value when recording fails or syncing becomes unreliable. Many users rely on Garmin devices for consistency, so unfinished behavior can significantly affect trust in the product.

ISM has worked like a charm for me, not having any of these issues, and been super reliable

Maybe you got a faulty unit and should claim warranty? 

One thing to keep in mind maybe: I like Polar watches, but their sleep tracking always conks out on me: at the same time loads of people have great experiences with Polar and call it some of the best sleep tracking in the business

Sometimes, some gadgets just don't work well with certain people maybe.

Btw, have you tried wearing it around your ankle for example?  

Also is it not recording sleep, or the syncing that is the issue? It might have to do with the type of phone your using? Different OS and stuff might cause some issues.

I would try connecting to a different phone maybe, and contact support, and discuss with them and ask for a new one maybe under warrant?y