The MOB+ system will not shut off the engine if the xFOB is only exposed to rain, splashes or a bucket of water.
The range in air will vary depending on the wireless surroundings of your boat from at least 50 feet, but if you fall into the water as in the ocean or a lake, the MOB+ system will detect a man over board situation and stop the engine. In this case the range in air does not matter and even 3 feet between the xHUB in your boat and your wearable xFOB will kill the engine when the xFOB enters the water.