On the website, you can add text that
they will receive along with the SOS signal and
GPS location.

Could that text include a link to a trip itinerary, participant information, equipment list, etc? The same sort of information that a backpacker would put in an "Open in case of" envelope before PLBs, SPOTs, and Sat phones.
_________________________
Hope for the best and prepare for the worst.

The object in life is not to be on the side of the majority, but to escape finding oneself in the ranks of the insane