I believe the 30 foot radius has mostly to do with the range of the bracelet. It's most like a bluetooth low energy device/connection and once you are too far away from your smartphone, the bracelet will lose connection. To the monitoring agency, it will appear the wearer just left their quarantine bubble/area without their phone and could be anywhere. If you can snorkel with your smartphone it would look like you are still compliant.
If the bracelet is using Bluetooth technology to transmit data the frequency used is 2.4 Ghz.
2.4 Ghz would not give any 30 foot radius through water, five feet is more likely.
My guess is that these bracelets will be used for land guests who quarantine in villas, but that's only my guess of course.
