ResMed makes a device called "S+" that is available through online outlets. I bought mine from [link removed] Amazon for $80. Put it on your nightstand. You tell it when you are shutting the lights out via your cellphone and tell it again when you wake up. You'll get a stage report almost instantly. There is a website that provides the information as well.
Beurer makes a device called "S-80" based on technology developed by EarlySense. It is a disc that is placed under your mattress. The operation is more or less the same as the S+ but we find it substantially more accurate, perhaps from the clinical trials done with the EarlySense hospital devices. I bought mine from [link removed] Amazon UK for about $190 since it was not (yet) sold here. Watch [link removed] for a US version perhaps. The EarlySense software (app on your cellphone) will identify potential breathing problems, which can be a tip to use Sleepyhead for the night in question if you don't do it daily.
Most likely the very best device for stage tracking is the Rythm Dreem. Unlike the above devices (and their competitors) which use respiration, movement and, for the Beurer at least, heart rate, the Dreem uses EEG. So You wear a headband instead. I suspect that because it uses EEG that it is the most accurate (consumer device) for staging. It's expensive, with shipping expect to pay $370.
None of these devices are eligible for (my) insurance reimbursement, but when I read about how long it can take to make sleep therapy work for people, I have made all three investments and use them all nightly. Note that Rythm do not want people with sleep disorders to be part of their current program (they are in a post-Beta, limited availability phase called Dreem First). Fortunately with my ASV, I don't have a sleep disorder anymore!
You will have to be somewhat picky about which CPAP mask you use with the Dreem. While I have used it with the Wisp (moderately comfortable), and the Dreamwear (quite difficult but I have made it work), I am experimenting with the P10 now.
The Dreem claims to increase deep sleep.
I keep a spreadsheet with data from my ResMed AirCurve ASV, the S+, the S-80 and the Dreem. Both the S+ and the S-80 are showing increased deep sleep percentages since I've been using Dreem. I expected it to report that but continue to double check. The Dreem works.
Some here may write about the Zeo which was also based on EEG, but that product and the necessary online support disappeared a while ago. You may also read about the Basis Peak smartwatch that used several sensors, but it was also recalled -- like the Samsung Note 7, it had a battery overheating problem.
You can track your sleep stages. I hope you will do it.
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