In boating, the kill switch is used in small outboard engines and looks like an extendible red cord. But there are also switch systems on the boat console.
In addition, there are MOB systems where the kill switch can be operated automatically in the event of the captain falling into the sea.
It is used to stop the engine in case of dramatic situations, bearing in mind that stopping an engine suddenly can pose serious risks to its operation and to the safety of people on board.