Movement Inc. Official Home Page
Most of the important 'metrics' that you need to track or measure need a notebook, notes app or some crude tracking method (app, Claude or whatever).
Measure your body composition once a year using a DEXA scan that is well calibrated.
Measure your strength by tracking a few lifts every few weeks. Or if you're truly obsessed, find a force plate to measure your jump or throw every year.
A mirror is a reasonable way to get a sense of how much fat you are carrying. If your mind plays games with you, get a tailor to give you your vital stats.
As for sleep, unless it's truly disturbed (in which case go to a sleep clinic), just fight to maintain a consistent schedule of hitting the bed the same time every single day.
Most of the objective 'measures' of progress can be measured by counting 1 through 15 or by using a watch.
There's context for an accurate heart rate monitor that has a strap tied around your chest to get an accurate read of what's happening when you exert yourself. But even this does not have to be daily behavior.
You really don't need a ring or a watch. Especially every single day. All day long. Especially not because of the emails Tim Cook gets about the Apple Watch saving someone's life. A visit to a competent doctor once a year would have sorted that out.
The watch winds up being a tool for the anxious, paranoid or impatient client to fixate on some strange metric. They'll say things like 'I still don't have a floor push up after 6 months like someone else' and go on a tangent about resting heart rate. Too many numbers and too little focus.
The only real device or virtue you need to succeed at the fitness game is patience and the capacity to do the same damn boring things for years on end. Helps if you start with a half-decent plan that doesn't change things for the sake of variety every other week. This applies to food, sleep and training.
Gadgets are not a substitute for discipline, consistency or a half decent plan. Most gadgets are just a symptom of our compulsive need to be seen measuring something or just involve technology in every waking moment or act of your life.
I am not some Luddite. Use tech to make a plan and track progress. Use the really good stuff like advanced blood tests, DEXA scans, doctors visits, ultrasounds, dopplers, MRI's, CAT scans etc as the doctor deems necessary to figure out what's going on. Electric motors are the future of lifting. They are incredibly nuanced in how they produce resistance. Force plates and bar speed trackers are objective tools athletes and serious lifters can use to eke out performance gains.
But a compulsive need to quantify or put a number or label on every habit, lift and movement is more likely to spawn obsessive, unsustainable behavior than healthy, sustainable habits.