EPIRBs are kept permanently in the “armed” position, and if the boat goes down, a water-sensitive switch triggers a radio signal that gets relayed by satellite to listening posts on shore. The Coast Guard immediately knows the name of the boat, the location, and that something has gone disastrously wrong. If a boat loses her radios before actually sinking, though, the captain can send a distress signal by just twisting the ring switch to the “on” position. It’s the same as screaming “mayday” into the radio.
