I read a story once about a chap who stowed his liferaft stood on end between the bunks in the forecabin for security on his mooring.
Before leaving the boat he used the heads .The wash from a passing mobo caused the raft to fall down wedging the strong hardwood toilet door solidly shut.
Several hours later he managed to pry the door open enough to reach a hand held vhf on a shelf.
Can you imagine the conversation with the coast guard,I wonder if he sent a pan pan(toilet pan that is)????
On a serious note,if you are below the waterline you may not get a signal on a mobile phone.
My hatch is held open by one of those large coiled springs that bend into a U shape when you bend it to close the lid. I think they are the dogs B’s, so much so that I put a mini one on the chart table lid to hold that open while rumageing the charts.