Emergency GPS: Precise Radio Beacons for Search and Rescue Services

Sometimes you might need to call for help if an accident occurs. You can use a cell phone to call for help, but you might be in a remote location with no cell phone signal. So one of the most reliable technologies you can use is emergency GPS.

 Emergency GPS involves using the US satellite network to locate beacon signals for search and rescue operations. You only need a locator beacon to send the distress signal, which makes contact with satellites to pinpoint your position. We will explain how the technology works and the types of beacons for different applications. Read on to learn more!

Table of Contents

What Is an Emergency Locator Beacon?

Also known as a radio beacon, an emergency locator beacon is a battery-powered portable radio transmitter used to locate persons in distress, vessels, or airplanes that need immediate rescue. This device gets activated when an emergency occurs (aircraft crash, ship capsizing, or people getting lost on a hike) and transmits a continuous distress signal as a radio wave. The GPS satellite network picks this signal and relays your location to search and rescue teams.

A personal locator beacon

A personal locator beacon

Emergency GPS: Types of Locator Beacons

There are several emergency locator beacon types in the market, each distinguished by its application area. The devices include the following.

  • Emergency Locator Transmitters (ELT): ELTs are aircraft locator beacons that signal crashes or distress. A plane’s crash sensor or G-force switch automatically activates the locator beacon in case of an accident, but pilots turn them on manually using a button in the cockpit.
An ELT access on a helicopter

An ELT access on a helicopter

  • Emergency Position-Indicating Radio Beacon (EPIRB): These are locator beacons for boats and ships that signal maritime distress. Water vessels have a manual switch for activating the beacon, but water can automatically switch the device on when it is outside its bracket.
An EPIRB outside its bracket on a ship

An EPIRB outside its bracket on a ship

  • Submarine Emergency Position-Indicating Radio Beacons (SEPIRB): SEPIRBs are EPIRBs approved for submarine use.
  • Ship Security Alert Systems (SSAS): These beacons signal distresses caused by piracy or terrorism. Personnel can activate it manually on the device or use a discreet button in the ship’s cabin/bridge.
  • Personal Locator Beacon (PLB): As the name suggests, these are compact, personal devices used to indicate a person’s location who is in distress. You can activate the device by deploying the antenna and turning the switch on.

Emergency GPS: Other beacons include the following.

The international COSPAS-SARSAT program receives and processes distress alerts from ELT, PLB, EPIRB, and SSAS. However, not all these types of beacons give GPS coordinates.


The COSPAS-SARSAT system has long been a model of international cooperation that began with the US and Russia. Over 40 countries joined later. The program’s monitoring includes three components: LUTs (Local User Terminals), MCCs (Mission Control Centers), and RCCs (Rescue Coordination Centers).

COSPAS-SARSAT beacons rely on the following types of satellites to provide location data.

LEOSAR (Low Earth Orbiting Search and Rescue Satellites)

This section of the COSPAS-SARSAT network uses the Doppler processing technique to calculate the origin of the distress alert. This technique bases its principle on the fact that the satellite’s relative velocity affects the locator beacon’s frequency. So the Local User Terminal (LUT) can calculate the beacon’s location using the known satellite position and beacon’s frequency changes.

A satellite in low earth orbit

A satellite in low earth orbit

GEOSAR (Geosynchronous Earth Orbiting Search and Rescue Satellites)

GEOSAR satellites remain in a fixed position relative to the earth’s rotation and use the GPS provided by PLB, ELT, and EPIRB to calculate the location of the distress messages.

A satellite constellation in geostationary orbit

A satellite constellation in geostationary orbit

MEOSAR (Mid-Earth Orbiting Search and Rescue Satellites)

These satellites are the newest addition to the COSPAS-SARSAT network and can detect distress messages plus the beacon location within five minutes with/without GPS. MEOSAR provides a framework for utilizing the RLS (Return Link Service) to deliver a confirmation message that help is on the way. And they can detect PLB, ELT, and EPIRB distress signals.

A flight data recorder with an ELT

A flight data recorder with an ELT

When either of these satellites detects a beacon signal, they forward it to one of the mission control centers. These centers determine which rescue center to send the alert to based on the beacon details and detected location.


Previously, the COSPAS-SARSAT system used the 121.5 MHz distress signal, but the network received a high number of false alerts that exceeded 98% of the received signals. So the COSPAS-SARSAT council decided to eliminate the 121.5 MHz repeater from newer satellites. Currently, the system can only detect 406 MHz beacons, which affects all personal locator beacons, aviation beacons (ELT), and maritime beacons (EPIRBs).

An airplane taking off

An airplane taking off

However, ground stations and airplanes still monitor the older beacon frequency because 121.5 MHz is still the official VHF voice distress signal for aircraft globally. And the FAA requires pilots to scan the channel wherever possible. 406 MHz beacons contain 121.5 homers. So they can monitor the channel.

GPS vs. Non-GPS Locator Beacons

Although Doppler processing works without GPS, it gives a relatively broad two-square-kilometer search area after trilateration.

But 406 MHz beacons with GPS increase the precision to within 100 meters, and the location service covers 70% of the globe’s surface closest to the equator.

However, a Doppler track must be available for rescue operations to commence. GPS only allows the geosynchronous, wide-view satellites to enhance the Doppler position from the low earth orbit satellites.

So COSPAS-SARSAT cannot resolve a beacon’s location until at least one Doppler track matches the encoded GPS track or two Doppler tracks match. GPS is insufficient on its own.

But the technology is only available in modern EPIRBs, which go by GPIRB. So ELTs and PLBs are yet to get GPS enhancement. However, PLB devices can have GPS receivers, giving them parallel systems that transmit your GPS coordinates and Doppler position.

An EPIRB in its bracket on a ship

An EPIRB in its bracket on a ship

Personal Locator Beacons vs. Satellite Messengers

Let’s delve away from the technical stuff a bit. When you want an emergency locator beacon device for personal use, you’ll mostly go for the PLB or satellite messenger. The devices don’t send signals on the same satellite network, so their fundamentals differ.


PLBs require beacon registration after purchase. The process is free and registers your device to the NOAA SARSAT database. So NOAA can associate a distress signal from the device to your name, contact details, medical conditions, emergency contacts, etc. You must update this data every two years and report any sale/transfer of ownership of the device to the database.

The devices also have a long battery life (up to five years). But once it dies, you must take the unit to a dealer for replacement because the cell is not rechargeable.

And since they operate on a government network for SOS reporting, PLBs have zero subscription fees. Additionally, the global network coverage means PLBs function anywhere on earth, although the response time from search and rescue teams can be slow in countries with limited resources. And some countries don’t permit their use. So you must do some homework to know if you can operate your PLB abroad.

However, these devices lack navigational features, 2-way messaging, and passive location sharing/tracking.

Typical ones include Ocean Signal RescueMe, ACR ResQLink+, and McMurdo Fast Find 220.

Satellite Messengers

Satellite Messengers are like privatized versions of PLBs. They use GPS data to determine the location information but have commercial satellite networks to enable their worldwide emergency communication system. These satellites route the distress signals through the GEOS IERCC, a privately-run emergency response coordination service based in Houston.

A GPS SOS location device above a topo map

A GPS SOS location device above a topo map

These devices have additional features like two-way messaging, navigation, non-emergency messaging, waypoint tracking, etc. However, you must pay subscription fees to use the commercial service, and the devices have a shorter battery life (10-20 days) due to all the extra features. But they have rechargeable batteries.

Typical ones include Garmin inReach Messenger, Zoleo Satellite Communicator, Somewear Hotspot, and Spot devices.

Wrap Up

In conclusion, GPS is critical for providing location information for emergency search and rescue operations. However, GPS data alone might be insufficient, so you need to combine it with Doppler processing or a communication system for better performance. That’s it for this article. Thanks for your time.

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