A safety system, which stops the motion of a boat or other craft when a person falls off the craft, is comprised of a wireless transmitter carried by the person, a receiver-controller, an actuator, and a spring loaded kill switch (ignition switch). When the person falls off and moves away, the diminution in wireless signal causes the actuator to remove a latch key or clip from the spring-loaded kill switch, thus stopping the engine. The actuator stores manually input energy, to enable the use of a compact and low power solenoid type coil. The system is suited for retrofitting onto boats having lanyard type kill switches.