I'll bet that an acoustic shutoff switch would not have been about to stop the oil spill at the BP rig in the Gulf. I suspect something is wrong with the blowout preventer itself. I thing this is true because the "dead man" switch didn't shut the valve and the remote vehicles weren't able to shut it either. I'll bet an acoustic switch would have been unable to get this probably broken device to function.in reference to:
"BP says the Deepwater Horizon did have a "dead man" switch, which should have automatically closed the valve on the seabed in the event of a loss of power or communication from the rig. BP said it can't explain why it didn't shut off the well."
- Leaking Oil Well Lacked Safeguard Device - WSJ.com (view on Google Sidewiki)