ELT (Emergency Locator Transmitter) Is a type of distress beacon used in aircraft activated automatically by the impact of an accident or manually via a remote control switch.
Once activated, the 406 MHz distress signal is transmitted continuously, alerting international rescue services to the emergency and your location via the global Cospas-Sarsat Search And Rescue satellite system and 121,5 MHz (homing), some also 243 MHz.
Some models have GPS or You can be connected to one.