The PanPan beacon connects trough the phone over a specialised long range bluetooth antenna.
It's an in depended system that does not require cellular connectivity.
Any iPhone 4s or higher or any recent Android (galaxy s3 or higher) will work.
For the past view months I've been hard at work to solve a problem my father in law had.
He was going on a sailing trip with his son that would require them to sail in shifts. Day and night.
The alternating shifts meant there is always a risk to fall overboard without the other...