EPIRB or Emergency Position Indicating Radio Beacon is a safety device carried by a vessel to alert search and rescue services, allowing them to quickly locate you in the event of an emergency. When activated it transmits a coded message on the 406 MHz distress frequency which is monitored by the COSPAS-SARSAT satellite system.
Credit: @BoatUSFdn
The Infographic above shows that when in distress in the middle of the sea, the seafarer has the chance to activate its EPIRB to send their information...