an apparatus provides a warning of propeller rotation or co / co 2 hazard in a marine craft and includes a sensor in communication with the propeller to directly or indirectly sense rotation of the propeller and to generate a signal in response to the hazard , a controller coupled to the sensor to process the signal from the sensor , and a sensory alarm coupled to the controller to generate a warning alarm signal when the sensor returns a signal indicative of a predetermined state of hazard , namely actual rotation of the propeller from a nonzero rpm to a user or factory defined rpm or co / co 2 levels at or above a predetermined maximum .