Man down saftey

Hello all,
Thank you for letting on the board.

I have an idea for a diver Down switch but can't seem to find a solution.

I'm thinking of using a 555 and a tilt switch to trigger a high pulse to an arduino to then trigger an sos LED flash.

So my thinking is this

Diver doesn't make a movement for 10secs the 555 sends a +3v high to the arduino.

But if there is some movement then the timer resets itself and no signal is sent.

Any ideas for this would be great many thanks