Apple Watch. Any watch with sleep and workout tracking would do (Garmin, Fitbit, etc). I primarily purchased the watch to help track my sleep and was shocked by just how bad my sleep habits were. I've improved my sleep patterns, increasing my average time asleep from 6:30 to 7:30 in two months.

A few added bonuses: the app I use for weightlifting (https://www.hevyapp.com/) has an Apple Watch mode, freeing me from my phone during workouts. I can also use the watch to track runs, as mentioned by the commenter in this thread with the Garmin Watch.