ExD
I have never heard of a sleep tracker, is it something you use with a smart phone? I'm one of those people who's phone isn't "smart", the cost (to me) doesn't seem worth it just to get the internet on another device when I have my tablet and laptop.
But a sleep tracker sounds amazing, I am a poor sleeper.
You can get them as wearable devices or as an app on a smartphone. A dumbphone doesn’t have the processing capacity.
My app can either use the microphone or the motion sensor. The microphone picks up and analyses all sounds including sheets rustling as I turn over and breathing (and records snoring, sleep-talking, and hears but filters out the background radio and the dawn chorus) (but it does occasionally analyse a heavy lorry roaring past as loud snoring!). If you use the motion sensor, you put the phone under the top sheet and it only picks up movements.
There is the option to measure heart rate when you wake using the torch and camera, but unlike a Fitbit or similar, it doesn’t monitor that continuously through the night.
In terms of monitoring sleep, it compares well with a wearable device when you use the microphone, but results with the motion sensor are a bit iffy. I wear a much loved analogue watch, and I wouldn’t consider a Fitbit or smart watch, so the phone app is a good solution for me. However, if you want to use a holistic health monitor, I guess a wearable would be better.