This app was mentioned in 4 comments, with an average of 2.50 upvotes
If you just want to track steps and have an Android smartphone, you should try Noom Walk. Very easy on the battery, and you don't need to buy an extra gadget.
IMO measuring calorie consumption accurately is an order of magnitude more important than measuring calorie expenditure: unless you engage in strenuous exercise for extended periods, additional expenditure from exercise << consumption, so errors in the latter are more significant. I tried various apps for calorie tracking, and found all of them tedious, so currently I am just using a spreadsheet.
Love my fitbit..... but apps like Noom Walk can track your activities... https://play.google.com/store/apps/details?id=com.noom.walk&hl=en
So if background apps can't access any sensors does that mean things like Noom Walk will no longer work