This seems like an over-engineered and failure-prone solution. A cheaper, more robust solution might be human lifeguards + medic-alert necklace with GPS. If y

This seems like an over-engineered and failure-prone solution. A cheaper, more robust solution might be human lifeguards + medic-alert necklace with GPS. If you pull off your necklace, it emits a screeching alarm, and you instantly show up as an emergency red blip to rescue. A decent enough Android smartphone costs like $20 at the low end. Surely a pool or beach could force guests to rent and wear these for a few bucks (or waive their rights to being saved).