Speaking of a convenience item worth it's price! EPIRB = Emergency Position Indicating Radio Beacon.

It's an emergency transmitter. Originally they used to send out a homing signal on emergency frequencies that were monitored by aircraft. Since the modern satellite area, in addition to the homing beacon, they communicate with the satellites to get the distress signal to the coast guard. There are different types; some even interface with or contain a GPS to send out exact positional data; some work only in coastal waters (these are being discontinued), some out to sea and all over the place. Even backpackers and hikers are beginning to carry them.