I've just bought a fitness tracker for £12.99 from Amazon. It syncs with my phone. I had a Fitbit that was around £90 but some of the info it recorded was, frankly, bizarre e.g. floors climbed 8, if I remember rightly, recorded while I was sitting at my laptop. They asked me if I had a window open nearby and maybe I was lifting my arms a la Liberace! ? Not long after that, the button fell out, too. I sent it back and got a full refund.
Having said that, it did inspire me to achieve a daily step count and that impetus dwindled after I returned it. Then, I got a Samsung phone and discovered the default Samsung Health app. It records steps and sets an activity target. Trouble is, I often forget to have my phone in my pocket. Anyway, the little wrist device came today and I've set it up. It tells me my heart rate and blood pressure as well as step count, calories burned etc. The great thing for me is that I can set it to buzz if I'm inactive for a set period of time. That's something I've wanted for ages.
I have yet to learn how accurate it may turn out to be. Watch this space but there are plenty of reasonably priced fitness trackers to be had on Amazon.