ELTs are emergency locator transmitters that are carried aboard most general aviation aircraft in the U.S. In the event of an aircraft accident, these devices are designed to transmit a distress signal on 121.5, 243.0-megahertz frequencies (and for newer ELTs, on 406 MHz).
This transmission is enabled automatically in the event of aircraft crash using G switch or by manual activation. With the use of ELTs the search and rescue teams can easily pin point the exact location of downed Aircraft.
The Emergency Locator Transmitter (ELT) is used to emit an emergency signal on 121.5 MHz, 243MHz and 406.025 MHz in the event of an aircraft crash. This signal will be picked up by the Search and Rescue Satellites (SARSAT) and processed. SARSAT then sends the information about the crash and location of the crash to the owner of the aircraft.

Below is an attachment that carries the report on Emergency Locator Transmitters