Question:
Is one allowed to wear an apple watch/fitbit on shabbos that counts your steps?
Answer:
There are two problems with wearing such a 2watch on shabbos, the fact that when you move you are activating the functions of the watch, which may be eiother boneh or make bepatish, and the display, which will be an issue of kosaiv. Secondly it is counting and measuring, which is also not allowed on shabbos, unless it is needed for ones health. Therefore it should not wear such a watch on shabbos.