Personal locator beacon

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.

Shop REI's selection of personal locator beacons and satellite messengers.

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 33,000 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.

Shop REI's selection of personal locator beacons.

How a PLB Works

PLBs transmit powerful signals at 406 MHz (MegaHertz), an internationally recognized distress frequency monitored in the U.S. by NOAA (National Oceanic and Atmospheric Administration) and the AFRCC (Air Force Rescue Coordination Center).

A PLB communicates with a network of Russian, Canadian, American and French military satellites known as COSPAS-SARSAT (SARSAT is an acronym for "Search and Rescue Satellite Aided Tracking").

After receiving your transmission, these satellites "fix" on your location using a Doppler Shift method and relay your information to the AFRCC where search and rescue procedures begin. If you use a GPS-compatible PLB, you can deliver your GPS coordinates very quickly without having to wait for the satellites to determine your position.

Personalized Signal

PLB owners must register their device with NOAA. When you do so, 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.

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.

If you use a PLB without a GPS, the 406 MHz signal from the satellite will get rescuers to within 2 miles of your position. Then search-and-rescue teams will use a tracking device to home in on the 121.5 MHz frequency. With this type of PLB in the continental U.S., it takes an average of about 45 minutes to alert search-and-rescue teams of your position.

If you use a PLB with a GPS interface, the 406 MHz signal will guide rescuers to an area less than 100 meters from your position. At the same time, they will employ a tracking device to home in on the 121.5 MHz frequency put out by the PLB. When using a GPS-compatible PLB in the continental U.S, it takes only 5 minutes to alert search-and- rescue personnel of your position.

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 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.

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. Keep in mind, however, that rescues generally come with significant pricetags.

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.

Key Features

Currently SPOT and DeLorme own the lion’s share of the satellite messenger market. Their key comparative claims:

  SPOT DeLorme
Messaging One-way Two-way
Character Limit 41 160
Message Confirmation No Yes
Satellite Network Globalstar Iridium
Min. Tracking Interval 2 minutes 10 minutes
Price Less expensive More expensive
Subscription Fees Yes Yes

This list offers only a basic comparison. Each device offers its own set of additional features as well. See product pages for details.

Shop REI’s selection of satellite messengers.

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