If you hear that call, it spooks you. So will the alarm that automatically sounds immediately if the wearer of the these personal transmitters falls in the water, breaking the radio transmission to the base unit onboard. Wire the base unit to a GPS, and it also will instantly record the man-overboard waypoint and help plot a course back to the man. The base station can keep six of the $99.49 transmitters charged. MOBi-lert 720i comes with two transmitters. $899; www.westmarine.com.