is there a device / system out there that ...

is not prohibitively expensive
can fasten a small receiver, that is waterproof, on a life vest, or on a body part, like a wrist ... and would be great if it had some kind of strobe on it
that will sound an alarm on the boat if one of these receivers goes more than a boat length away
sends back a LAT LON position to some instrument on board
sends a GPS signal every whatever minutes so others thousands of miles away can keep track of position en route
has the ability to send a short text message along with the GPS position spot, but not using WINLINK and the SSB

???

my son is looking for something as part of a school project for the next cruise we do this spring, something his classmates can follow ... and keep us safe in the process. We often are doing 2-3 day overnight passages, most the night only one person is awake, it would be nice to know if someone went over the rail while taking a piss at 3 AM ...

I've seen Raymarine's LifeTag and the SPOT, but I don't think either does ALL of the above ...

thanks, cheers, John