Emergency Position Indicating Radiobeacon Station (EPIRS or EPIRB) or Personal Locator Beacons (PLB), are small, portable transmitters that can be activated in an emergency situation and send out alarm signals.
The alarm signals are received by orbiting or geostationary satellites and forwarded to an operations control center via a ground station. Since the emergency radio transmitter is equipped with a navigation system (e.g. GPS), a satellite can receive the alarm together with the current position of the PLB and forward it to the operations control center. With such a device, it usually takes a few minutes before the operations control center is alerted. The emergency beacons send a device-specific code with which their owners can be identified via a directory. For this purpose, the owners of the devices must register with the responsible national organizations, for a fee. Because "visual contact" must exist between the PLB and the satellite in order to transmit the emergency signals, a PLB can only function reliably in open terrain. Since no voice communication is possible with a PLB, the operations center does not know what type of emergency it is. It must therefore assume the worst. The exact location of the emergency may have to be determined by special direction finder planes and / or helicopters with direction finding devices. Rescue can become expensive as a result. A satellite phone may be more suitable for alerting you in an emergency.
Most satellite phones have a dedicated emergency button. However, the user must assign an emergency number to the key in advance. This can be, for example, the national emergency number of the country in which the user is currently located.
In some countries around the world, radio frequencies can be used by anyone to call an ambulance service. However, the devices used for this have to meet precise technical specifications in some places. In Switzerland, for example, radio devices that are used exclusively for emergency calls (with a built-in "REGA chip") are exempt from the license requirement. Only conversations about the rescue are allowed. The operation of radio devices that do not comply with the regulations is not permitted there.
I will shortly be writing a page with the most common emergency radio frequencies for civilians.
PLB device supplier: https://www.acrartex.com