If the personnel of the Dive Center or even your loved ones look for you, give them the serial number of your SharkNet device (S/N) that you find in the back of the device (it’s strictly private: it’s not found in the web site!!).
They’ll be able to send you a SMS: if you are at the surface, the device will communicate them your position. If you are still underwater, it will do that a soon as you resurface.
…our underwater peacefulness often depends also by the one of those who remained at the surface.
To allow those who try to send you a position request and to see on the map where you are, the easiest thing is that they also download the Sharknet app for free and register as “family / friend”.
So in the section of the App SETTINGS >> CHARGE MY SHARKNET can load credit to send you the SMS requesting your position: just add the amount you prefer (eg € 20) through their PayPal account.
Each SMS requesting your position (or the position of any Sharknet of which they have the number) costs € 0.20; the cost will be deducted (and registered to be able to consult the expense history) from the credit charged on the App.