Personal locator beacons (PLB) are satellite devices that transmit a distress signal to search and rescue organisations once they are activated. Because they transmit the signal via satellites they can be used in remote locations, where no cell phone access is available. They are related to EPIRBs (Emergency Position-Indicating Radio Beacons), which are mainly used in boats and ships and are normally permanently installed in a vessel. PLBs are much smaller and lighter hand-held devices intended to be carried by a person.
In the following I am going to argue that they are a useful addition to the equipment list for anyone who is away from emergency services and is out of cell phone coverage. In particular, they are incredibly useful for anyone who is exercising some potentially dangerous activities in a remote outdoor setting. That includes activities such as hiking in remote wilderness areas, mountaineering, rock climbing, kayaking and so forth. Especially if they are carried out solo, that is by a single person alone, it is highly recommended to carry a PLB.
PLBs are designed as a form of backup communication in case all other options fail when a person is in a life-threatening situation. If cell phone reception is available, or any other form of two-way communication such as CB radios, that is the preferable option.
On the technical side, nearly all currently available PLBs include a GPS receiver. Once activated the PLB transmits its GPS position to the satellites at a frequency of 406 MHz together with other information about the device including its registration number, which is linked to the owner. The integration of a GPS device has the advantage that a much more accurate position is available to the rescue services. That means that they need to search a much smaller area and will find the person faster. In addition to the 406 MHz satellite signal, most devices also transmit a homing signal at 121.5 MHz.
Most PLB models utilise the COSPAS-SARSAT satellite system, but there are others that use the Iridium satellites and offer two-way communication via text messages. Some of them require a monthly subscription to keep the device active. The majority however are free after the initial purchase of the device.
The good news is that PLBs can be hired for a small fee from some national park service centres in Australia. However, if you use it often it makes more sense to buy one.
If you venture into remote wilderness areas I would strongly recommend investing in a PLB. More so if you do that solo, or in a small group only. It will likely be the only way that you can alert emergency services in case of a serious injury, snake bite, etc. Even for trips into less remote wilderness areas the convenience that you can stay with an injured person, instead of having to search for a place with cell phone reception makes it worth having it.