I've used (a) the Beddit touch-sensitive mat, (b) the Fitbit watch, and (c) the Oura ring. Beddit claimed I never slept more than 2 hours a night, which was something of an exaggeration. Fitbit was better, but I still caught it a couple of times claiming that I was asleep when I was actually lying awake reading for an hour. I've been using the Oura ring for maybe 6 months and I haven't caught it in any known mistakes so far; there was one weird thing where if you had multiple sleep periods separated by several hours, it'd show only one of them in the cloud view, but I've not hit that recently.
I would recommend the Oura ring with few reservations.
I have a Xiaomi fitness band 2. As far as I can tell, the sleep metrics it reports are pretty good. I wouldn't attempt to compare its accuracy to an Apple watch, but the Xiaomi's battery charge lasts about a week and it cost $30.
I'm really impressed with Mi Band 2 sleep tracking. It correctly matches the time I go to bed, and get up. Also gets each time I wake up during the night, or when I'm reading before sleep. I'm not sure about the "deep sleep" recording, and maybe I'm being suggested, but in nights with low deep sleep I fell terrible. Just monitoring my sleep I improved it. Sorry that it does not have a smart alarm neither an alarm to go to bed.
Withings (ex Nokia) is selling mats that you put under your sheets and where you lie on. I think Apple does, too, but only in America.
That's probably the best device for home-use. But sleep labs are using EEGs, cameras, microphones and puls oxymeters for a reason. Don't expect medical-grade results from a home-use device.
Less accurate are several kinds of fitness trackers/smart watches, very inaccurate are smartphone apps.
I wish the Withings mat would have the option to wake me up when optimal time comes. I had a fitness tracker that did that but it was very subtle and started working after a few weeks.
Are you thinking of the Pebble watch? Maybe in combination with some Android app? I had this setup years ago and I do miss it. I'll have to see whether it can be replicated with my current Fitbit, last I checked it couldn't but it was a while ago.
