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RMRG is a fully
accredited Mountain Rescue Association (MRA) team

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Emergency personal beacons: A primer

From late December 2009 through February 2010, the Rocky Mountain Rescue Group was involved in a search for a Personal Locator Beacon (PLB) that was being used incorrectly. The beacon was first activated on December 14, 2009 in the Berthoud Pass area, triggering an emergency response from multiple law enforcement and mountain rescue agencies. The beacon was deactivated before rescuers could find the owner. In the ensuing two months, the beacon was sporadically activated in various locations in Colorado.

On February 11, 2010, the beacon was again activated on Berthoud Pass, but this time was not turned off. The beacon was tracked along the I-70 corridor, indicating it was in a moving vehicle. Upon learning of the beacon's status, RMRG was paged and deployed radio tracking resources in an effort to find the beacon. Using specialized radio Direction-Finding technology, members of RMRG tracked the PLB to the owner's car in downtown Boulder. RMRG then learned that the beacon owner, a backcountry skier, had been activating his PLB while skiing potential avalanche terrain, confusing his PLB with an avalanche beacon, and not understanding that his PLB device was designed to be used in emergencies only. The Clear Creek County Sheriff's Office, which had jurisdiction in the case, ultimately declined to file charges against the PLB owner for misuse of the device, but did ensure that owner finally registered his PLB [News/blog links: link 1, link 2.

RMRG has created this web page to educate the public about PLBs and their appropriate use. Please note that RMRG does not endorse commercial products. This page is informational only, and is provided to assist people who are interested in purchasing PLBs or SPOTs.

(NB: This page was written in March 2010 and may not be updated in the future, so specific features of beacons described here may have changed since this writing.)

Any person who ventures beyond a trailhead should notify a trusted emergency contact of his or her plans in case there are problems. Do not rely upon PLBs, SPOTs, ham radios or cellphones to always work.

About personal emergency beacons

Emergency alert beacons are small, handheld devices that can alert appropriate authorities to a wilderness or marine emergency. For wilderness use, there are two main types of beacons: Personal Locator Beacons (PLBs), which work on the COSPAS-SARSAT network, and the SPOT beacon, which works on the GEOS network. PLBs and SPOTs have been used successfully to direct rescuers to emergency backcountry situations, but both systems have their limitations, as well as their differences.

Before we go further into the details of beacons, three notes of caution:

First, since these are electronic devices and rely on batteries, complicated circuits, satellites and ground based systems, their use does not assure that assistance will be timely, and they may not work at all when you really need them. The use of PLBs, SPOTs, or other devices should only be viewed as a way to send out a call for help when you have no other options. They should not be used other than in true emergency situations. RMRG provides an online Safety in the Mountains brochure that discusses safety concerns when going into the backcountry.

A second note of caution: purchase of these beacons requires registration of the beacon before first use. The SPOT will not work without first being activated and registered. Other PLBs, however can be used without registration, but we highly discourage this. In case of a real emergency, not having registered your PLB before your trip significantly decreases the chance of a successful rescue. A registered PLB or SPOT allows rescue teams to gain valuable information from your emergency contact about your trip objectives, number in the party, possible medical conditions, gear you are carrying, etc.

Third, PLBs and SPOTs are not avalanche transceivers or beacons. Avalanche transceivers transmit and receive on a completely different frequency (457 KHz) and are typically received by similar units, carried by companions, less than 100 meters away. This frequency transmits well through snow, unlike the PLB or SPOT transmissions. Avalanche transceivers are intended to facilitate the rapid location by a nearby companion of a person who has been trapped under snow in an avalanche. Avalanche transceivers do not transmit to satellites. PLBs and SPOTs do not transmit well through snow and are not received by other PLBs or SPOTs. Avalanche transceivers are valuable and potentially life saving devices for people traveling through areas where avalanches are possible.

The nuts and bolts of personal beacon systems: PLBs and SPOT

[Note: RMRG does not endorse commercial products and no implications favoring one product over another should be taken from this page.]

PLBs and SPOTs are popular products and both can be (and have been) very useful devices for backcountry emergencies, but it important to understand their similarities and differences. First, the key similarity: Upon activation of their emergency modes, both the SPOT and PLB systems attempt to communicate with a rescue coordination center (RCC) via satellite. The RCC receives the signal, processes it and gathers as much information as possible, and then passes notification along to the appropriate local rescue agency (in the case of Colorado, the Colorado Search and Rescue Board is first contacted, which then contacts the local Sheriff).

Personal Locator Beacons

Upon activation of the emergency mode, PLBs send a 5 watt signal to the COSPAS-SARSAT satellite network on the standard emergency radio frequency of 406 MHz. For inland emergencies in the U.S., the U.S. Air Force Rescue Coordination Center is the RCC that receives and processes the signal. Lacking any other information (i.e, GPS coordinates also transmitted), the 406 MHz signal can help the RCC locate the signal to within 2-3 miles.

In addition to the 406 MHz satellite signal, modern PLBs also transmit a homing signal on 121.5 MHz (a long-standing emergency frequency; an emergency distress signal is also transmitted on 121.5 MHz when a small airplane crashes) and some are also equipped with a GPS. The 121.5 MHz homing signal is for field teams equipped with radio Direction-Finding (DF) technology to more easily find the beacon. (RMRG maintains equipment and a high level of competency for DF missions, but not every mountain rescue team is so fortunate.) PLBs equipped with GPS attempt to also send accurate coordinates to the RCC, allowing for pin-point location accuracy in many cases. The most effective PLB will have 406 MHz, 121.5 MHz and a GPS. Note that some very old "PLB" units only transmit on 121.5 MHz and do not transmit on 406 MHz. Other devices use the name "Personal Locator Beacon," but are not COSPAS-SARSAT compliant.

On the other hand, some newer PLB's include capability to send messages such as "I'm OK" and mapping information to friends. These messages are transmitted on the regular COSPAS-SARSAT satellite network.

Drawbacks: Many PLBs have some limited self-test features, but most PLBs' functionality can only be verified at a system level at the time of an emergency. For most units, PLB activation means "life threatening emergency" and thus should only be used when an emergency is happening. (Do not activate it for fun or testing!) The PLB self-test can only be used sparingly as it depletes the batteries. One PLB type can only be self-tested once every 6 months. The expensive PLB battery must be replaced every 5 years regardless of use. Failure to maintain the battery properly means that the beacon may not work when needed.

If you get a PLB, we strongly recommend that you purchase one that is COSPAS-SARSAT compliant, has a GPS, and transmits on both 406 MHz and 121.5 MHz.

SPOT and Satellite Communication/GPS Only Beacons

The SPOT system uses a higher frequency (1610 MHz) to communicate with its RCC, which is operated by Globalstar (a NASDAQ-listed for-profit company). The SPOT does have a GPS, but does not transmit a homing signal on 121.5 MHz. While the 5 watt 406 MHz signal used by PLBs can be used to get an approximate location (within 2-3 miles), the SPOTs 1610 MHz signal is transmitted at weaker power and cannot be used for an approximate position. Therefore, in emergency communication, the SPOT relies solely upon the GPS for transmitting location information.

The SPOT must have a line-of-site to the sky both to acquire position with the GPS and to send a message to satellites. This reduces their coverage as compared to the PLB. (In light forest they might work, but in heavy forest in a deep canyon they may not.) It is possible that a SPOT might send a distress alert without a location, or with an inaccurate location, illustrating the importance of leaving trip itinerary information with a trusted emergency contact known by SPOTs RCC.

While the SPOT has reduced coverage compared with PLBs, there are other things to consider that make it useful to have. The SPOT can be used to send "OK" messages to your trusted contact. This keeps folks at home assured of your well-being and location. It can also mitigate some coverage concerns because you can send "OK" messages in good locations and if a problem happens where you cannot send a message, then after a time (like overnight) your trusted contact can initiate an (albeit delayed) emergency response. If you are prepared to stay overnight, as you should be, then this is a reasonable outcome. Your previous "OK" messages can be used by searchers as a "last known location" to start a search for you. The "OK" message feature also allows the SPOT to be tested at home and in the field at various locations. This can build confidence that the SPOT will work when you need it to. Deep forest situations can be tested. The SPOT batteries are simple lithium-ion designs that are user-replaceable, so spare batteries can be carried. The SPOT 1 can be configured to send a "Request Assistance" (aka "Help") message that is distinct from the "Emergency Response" (aka "911") message (the SPOT 2 has this as a devoted feature). The "Request Assistance" message is useful in that it conveys enough of the nature of the situation that a full emergency response is not required. It is good for getting a little help via a trusted friend or an outfitter rather than launch a full rescue response. From a rescue standpoint, any communication that can convey the nature of the emergency can help define an appropriate rescue response. Features like "OK" messages, field-testing and "Request Assistance" messages that augment the typical "Emergency Response" message are useful attributes.


Empirical data of rescues show that both PLB and SPOT technologies are effective if maintained and used properly. If the GPS in the unit gets a GPS lock, then the location provided to rescuers is very precise and little "searching" is required as long as the user does not move. Both technologies can suffer from user error as well. This is typically caused by an emergency activation when there is no real emergency. This causes the needless deployment of rescue resources. Many PLBs are not registered and thus there is no emergency contact information associated with them and this causes problems when there are sporadic activations.

The satellite system for PLBs is the same system used by worldwide Maritime EPIRBs and thus many nations are vested in its performance and reliability. The SPOT devices are using a private satellite communication system with partial world coverage. You will need to evaluate the multi-government satellite system on one hand vs. a commercial for-profit satellite system on the other with regards to reliability and longevity. This may or may not have any future implications as to the utility of the technologies for yourself and where you want to use the device.


It is hard to compare costs between PLBs and SPOT since the feature set is different between the technologies. Besides the initial unit cost, PLBs require expensive battery changes that need to be considered, while SPOTs have a subscription fee for emergency and non-emergency features. Both are affordable for much of the recreating public. Frivolous use of a PLB or SPOT can lead to fines or legal troubles. Note: The Rocky Mountain Rescue Group does not charge people for call-outs regardless of the degree of the emergency.

Biggest search and rescue issues

Ultimately, if you own and then activate a SPOT or PLB in a true wilderness emergency, you are doing so under the hope that you will be rescued in a reasonable amount of time. It is to your best advantage to help us help you make your rescue successful. From the perspective of a mountain rescue agency, these are the most problematic issues regarding emergency beacon activation:

  • User errors such as activating a full emergency response by accident or when not necessary.
  • Users not knowing how to use the device properly causing sporadic transmissions, inconsistent messages or message cancellations.
  • Not telling a trusted emergency contact your plans.
  • Not registering your device or not keeping the emergency contact information current.
  • Not telling your trusted emergency contact what to do for the various messages, message cancellations, or absence of OK or Tracking messages that the device might produce.

    As with any equipment you trust your life to, take the time to learn about any device, and how to use it expertly. These devices should not be viewed as a license to make poor decisions in the wilderness. They may assist rescuers in reaching you, hopefully before it is too late.


    Mountain Rescue Association Meridian Newsletter, January 2012: Satellite Messenger Units Overview PDF, see page 9.

    Clear Creek County Sheriff press release on Berthoud Pass beacon case

    Manufacturer's Proponent PLB Discussion

    Manufacturer's Proponent SPOT Discussion

    Cospas/Sarsat Info

    PLB Registration

    SPOT Registration

  • This page is superseded Visit our current web site at http://RockyMountainRescue.org

    Rocky Mountain Rescue Group, Inc.
    3720 Walnut St, Boulder, CO 80301, USA

    Copyright 2017, Rocky Mountain Rescue Group, Inc.