Hi Fiona. Welcome to justanswer.
Which phone are you using? And also specify which activity tracker you want to use?
Fitbit is the best option to choose from the available fitness trackers in the market and it is compatible with your Sasmusng phone. There are so many models from fitbit. You can choose any according to your requirement
When you check any device, in its tech specs, it is clearly mentioned that it supports Android version xyz or higher. And you can check your phone`s OS (android`s) version by going to SETTINGS-ABOUT PHONE. The android version will be mentioned there.
Fiona, on your phone, Press MENU. Then go to SETTINGS. Do you see ABOUT PHONE (last option on the list)?
Anything that says compatible with Android 4.1 or higher will work fine with your phone
Fiona, do you have any other query?
Yes you can try others. If you get any difficulty then you can ask me. I will tell you if it is compatible or not.
You will see a tab on your screen saying WRITE A REVIEW. A positive review is well appreciated. Thanks