How do rescue beacons work?

//How do rescue beacons work?

How do rescue beacons work?

Distress beacons are small, lightweight devices that can alert search and rescue services of an emergency and can significantly decrease the time and effort required to locate a missing person or persons. It almost goes without saying, that anyone undertaking outdoor activity should be carrying one of these devices on them.

When you activate a PLB, the PLB unit will transmit a distress signal that is picked up by dedicated satellites (the Cospas-Sarsat System). This transmission is relayed to an Australian government agency, who in turn pass on details of the transmission to local search and rescue services that conduct the actual search and rescue activity.


  1. Beacon Activation

When you activate your PLB, the unit starts to transmit a radio signal in bursts at 406MHz and 121.5MHz. Only the 406MHz signal can be picked up by Cospas-Sarsat satellites. As satellites rely on direct line-of-sight, you should try to ensure you PLB has an unobstructed view to the sky. Deep canyons, or buildings may impact the ability of the satellite to pick up a signal. If underwater or in a cave, the transmission is unlikely to be picked up at all.

  1. Satellite Detection

Within a few minutes, the distress signal will be picked up by one of ten dedicated Cospas-Sarsat satellites above the earth’s surface (see The International Cospas-Sarsat Programme below). The signal will include the specific HexID or Unique Identification Number (UIN) of your unit and (if equipped) the GPS coordinates of the unit. The satellite will relay the distress signal to the nearest Local User Terminal (LUT).

  1. Transfer to LUT

There are now forty countries participating in the Cospas-Sarsat System. Each of these countries maintain Local User Terminals (or LUTs) to receive, analyse and process signals received from Cospas-Sarsat satellites. In the Australian search and rescue region, LUTs operate in Albany (WA), Bundaberg (QLD) and Wellington (NZ), and are all coordinated within the Australian Joint Rescue Coordination Centre (JRCC) or Mission Control Centre (MCC) in Canberra.

  1. Transfer to MCC

The signal, including any location information and registered information, is transferred to the nearest Mission Control Centre (MCC). In our region, the MCC is in Canberra. These local centres coordinate with local government search and rescue services. The information that is now available to rescue services is the estimated location of the distress signal, the country in which the unit was registered, and any information registered with the home country (see Registering a PLB below).

  1. Local Authority Search and Rescue

Local authorities, equipped with the beacon location details will then use specialised equipment and hone in your location using the 121.5MHz signal. For this reason, it is important that once activated the PLB remains turned on until rescue services arrive.


121.5 MHz beacons

In 2009 the frequency in which beacons communicate to satellites changed. These older beacons are no longer detected by satellites. You should ensure your beacon transmits at 406MHz.

GPS vs Non-GPS

One of the most significant difference between different PLB units on the market is whether the unit includes or excludes GPS. Both units perform the same service, however there are significant benefits of a GPS enabled unit.

GPS enabled Non-GPS
Alert time Detected within minutes Detected within minutes
Time to provide location Up to 20 minutes Between 90 minutes and 5 hours*
Precision Within 120 metres Within 5 kilometres

*Without GPS coordinates a satellite must pass over the signal twice and successfully confirm the beacon signal. As satellites don’t follow the same path, it can take anywhere from 90 minutes to 5 hours before a satellite will pass back over the same location. Even then, the location is generally only within 5 kilometres.

Using a PLB Overseas

A PLB is designed to work anywhere on the earth’s surface. Therefore, you can use your PLB while overseas. However, remember that all rescue services will be managed and coordinated using local search and rescue services. Australia will not be involved in the rescue, although the Australian Maritime Safety Authority (AMSA) will provide any registration details you have provided and any information gathered from contacting any listed emergency contacts. AMSA will also request information regarding the progress of any search and rescue.

Finally, you should also check the country in which you plan to take your PLB as some the use of PLBs on land is illegal in some countries.

Using an Overseas PLB in Australia

Internationally purchased PLBs can be activated in Australia and Australian search and rescue services will coordinate any rescue response. The country where the beacon is registered will also be notified.

Registering a PLB

While you can still use an unregistered PLB and rescue services will still come to your aid, by registering your PLB, you can you provide additional relevant and important information. This can include personal details, next of kin details, travel details, and other information that may be relevant to search and rescue services. This information is made available to the local search and rescue services to assist in their efforts.

In Australia PLBs are registered and managed by the Australian Maritime and Safety Authority (AMSA):

If you buy or sell a second-hand PLB, you are required to notify AMSA of these changes.


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