How to Choose PLBs and Satellite Messengers

 Image showing three examples of PLBs and satellite messengers

While deeply rewarding, backcountry adventures also entail risks that can occasionally prove life threatening—even for the most experienced outdoor enthusiasts.

Technology has come to the rescue with:

  • Personal locator beacons (PLBs): Available in the U.S. since 2003, these satellite-based handheld devices provide a powerful safety net for wilderness travelers.
  • Satellite messengers: A more recent innovation, these handheld devices—such as those from SPOT and DeLorme—have evolved to offer additional backcountry communication options.

Though both are portable transmitters, personal locator beacons and satellite messengers have some important distinctions. This article covers the basics of each.

Personal Locator Beacons

Personal locator beacons are high-powered (typically, 5 watts) devices designed primarily to send out a personalized emergency distress signal. They generally require an open view of the sky to transmit successfully.

PLBs are the land-based equivalents of Emergency Position Indicating Radio Beacons (EPIRBs), a technology that has been in use for decades in marine environments. Over the years, these devices are estimated to have saved more than 43,000 lives.

Important: A Personal Locator Beacon should be activated only in situations of grave and imminent danger, and only as a last resort when all means of self-rescue have been exhausted.

How a PLB Works

No matter where you are in the world, when you activate a PLB, it transmits a powerful signal at 406 MHz (MegaHertz), an internationally recognized distress frequency monitored in the U.S. by NOAA (National Oceanic and Atmospheric Administration), the AFRCC (Air Force Rescue Coordination Center) and the USCG (United States Coast Guard). The signal is sent to a network of American, Russian, Canadian and French weather and global navigation system satellites that are part of the COSPAS-SARSAT international satellite-based search and rescue system (SARSAT is an acronym for "Search and Rescue Satellite Aided Tracking"). COSPAS-SARSAT uses a constellation of satellites, known as MEOSAR (Medium Earth Orbit Search and Rescue), which allows for near instantaneous detection of the PLB signal and the ability to locate the PLB without GPS-encoded information anywhere in the world.

After receiving your transmission, the satellites "fix" on your location using frequency of arrival (FOA) and time of arrival (TOA) methods, then relay your information to the AFRCC or the USCG depending on the location of your alert. If you use a GPS-compatible PLB, it can deliver your GPS coordinates to search and rescue personnel through the satellite system. This information is passed on to local search and rescue authorities who will come to your assistance.

Personalized Signal

Federal law requires that all PLBs be registered in the NOAA SARSAT (Search and Rescue Satellite Aided Tracking) database. Registering your device is free of charge and the data is protected and only shared with rescue forces when your PLB is activated. When you register, NOAA will link your essential personal information to a 15-character code known as a Unique Identifying Number (UIN). When activated, the PLB transmits your UIN to the COSPAS-SARSAT satellites via electronic bursts.

While the electronic bursts provide search-and-rescue units with your location, the UIN tells them personal information such as your name, address, phone number and any medical conditions you may have.

You can register your device and update personal information at

Two Types of PLB Signals

When activated, a PLB sends 2 signals: 406 MHz (which carries the UIN and GPS data to the satellites) and 121.5 MHz, a homing frequency.

The 406 MHz signal from the satellite will get rescuers to within 5 kilometers of your position. Then search-and-rescue teams will use a tracking device to home in on the 121.5 MHz and the 406 MHz frequencies. GPS-compatible PLBs also deliver the GPS coordinates of your position (accurate to to within 500 meters) to search and rescue personnel through the satellite system.

Note: REI carries only models with a GPS interface.

Keep in mind that it's always a good idea to have a visual and/or audible distress signal such as a signal mirror, whistle or strobe light to help catch search and rescue's attention when they get close. Many PLBs include a built-in LED signal light for this purpose.

How Long Will a PLB Transmit?

A PLB comes equipped with a long-lasting lithium battery. This battery remains dormant until you flip the switch to activate the PLB.

By COSPAS-SARSAT regulations, a PLB must transmit for this amount of time:

  • A class 1 heavy-duty battery must be able to transmit at -40°F (-40°C) for 24 hours.
  • A class 2 battery must be able to transmit at -20°F (-28.9°C) for 24 hours. (Most PLBs for recreational use have a class 2 battery.)

Cold temperatures will shorten a battery's operating time, and the situations above represent worst-case scenarios. For example, at a temperature of 70°F, these batteries will operate for approximately twice as long as they will at very cold temperatures.

REI currently carries PLB models from ACR Electronics.

No Subscription Fees

Unlike with satellite messengers, you do not have to pay any recurring fees in order to use a PLB.

Satellite Messengers

SPOT sat messenger

Much like PLBs, satellite messengers are handheld transmitting devices that are useful in backcountry areas far from reliable cell phone coverage. These user-friendly devices allow you to communicate short text messages and/or your location coordinates with friends or family back home so you can report on your trip’s status or, in an emergency, send calls for help.

While a handy tool for casual hikers and backpackers, satellite messengers transmit signals that are much less powerful than a PLB signal. They are not intended for serious mountaineering use.

How a Satellite Messenger Works

Satellite messengers are GPS-based devices that rely on either of 2 commercial satellite networks—Iridium or Globalstar—rather than the military network used by PLBs. Emergency calls using either network are routed to the privately run GEOS International Emergency Response Coordination Center headquartered near Houston, Texas.

A subscription fee is required to use a satellite messenger. Each manufacturer offers a variety of usage plan options, usually including duration (yearly, seasonally or monthly) and GPS tracking frequency (with intervals ranging from hours down to a few minutes).

What are the differences between the satellite networks?


  • Used by DeLorme devices.
  • Offers 100% planetary coverage via a 66-satellite network.
  • Uses 2 ground-based gateways (rather than satellites) process and switch messages.


  • Used by SPOT devices.
  • Covers most of Earth’s land masses (except polar regions and sub-Saharan Africa) via a 48-satellite network.
  • Uses 24 ground-based gateways to process and switch messages.

Note: Satellite messenger devices are considerably less powerful than PLBs and virtually always require an open view of the sky to transmit successfully.

Each satellite network has its share of fans and detractors relating to their ability to deliver messages 100% of the time. At this point, the jury is still out.

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