There is some confusion around the change to Law 4 - The Player's Equipment. The law reads:

The first paragraph is the source of the confusion around this rule update. People read “Electronic performance and tracking systems” and think “Oh, that’s what my fitbit does!” However, that is not the case. Just check out these descriptions of a EPTS from the FIFA website: https://football-technology.fifa.com/en/media-tiles/electronic-performance-and-tracking-systems-epts/ and https://football-technology.fifa.com/media/1031/epts_english.pdf. Note that from reading these descriptions, it is pretty clear that a fitbit device, capable of working as a device that can measure heartrate and other physiological parameters, can be part of the system, but it is not an EPTS by itself. Fitbits are Wearable Technology only. The AYSO Regions in the Cedar Rapids area do not have an EPTS. Thus, fitbits and like devices are not allowed any more than we allow watches or friendship bracelets.
Excellent question! This posting came about because I had a player try to insist that a fitbit was now legal, and also heard from the adult league that the word was that they were legal. So this is primarily to nip that misconception in the bud.
A referee can wear a fitbit, after all, it is your "back up time keeper". Remember, wristwatches are preferred over stopwatches or cellphones. Watches are more accessible and easier to manage on a busy pitch.
Please do police yourself on other jewelry. Wedding rings are fine, as long as they are bands without stones, i.e. nothing sticking out to scratch a player. Removing necklaces, earrings and other such items sets a good example for the players, and makes you look more professional in addition to any safety concerns.
I know there are restrictions on Referee Equipment as well. Are you asking us just to remain diligent in asking players to remove the devices, or are we also asking Refs to double check themselves (equipment+jewelry) before entering the pitch?