PLB stands for Personal Locator Beacon. About a year ago, after giving it a lot of thought and after doing a lot of research, I bought a GPS-Enabled 406 MHz PLB: the one I chose is an ACR ResQLink. So why didn’t I buy a SPOT, instead? Over the past month, I’ve had a number of hikers ask me that question and I’ve given them the reasons based on my research.

Given all the questions, I thought it might be a good idea to post my research and reasons on my blog where it’s easily accessible to others who might find it helpful. This is a hiking blog and since, for me, the purpose of a personal locator beacon is to get rescued, I will only focus on features related to emergency distress signals.

First things first: 1) What is a PLB?, and 2) What is a SPOT Messenger?

1. A PLB is a battery-powered, electronic device-of-last-resort that, when activated, will attempt to send a distress signal, along with your GPS location information, to a satellite for the purpose of notifying local search-and-rescue of a life-threatening emergency to you (or someone in your hiking group) with the implied need for an immediate rescue.

ACR ResQLink Personal Locator Beacon

ACR ResQLink: Personal Locator Beacon

2. A SPOT Messenger (hereinafter as SPOT) is a battery-powered, electronic device-of-last-resort and a messaging device-of-first-resort that, when activated, will attempt to send a variety of custom, pre-programmed text and/or e-mail messages (such as Help/Assist, OK/Custom, Track Progress), depending on your subscription plan(s) to a satellite for the purpose of notifying personal contacts of your status — OR — will attempt to send an SOS distress signal, along with your GPS location information, to a satellite for the purpose of notifying local search-and-rescue of a life-threatening emergency to you (or someone in your hiking group) with the implied need for an immediate rescue.

SPOT Messenger Locator Beacon and Messaging Device

SPOT Messenger: Locator Beacon and Messaging Device

Based on the feature set alone, you would think SPOT was the clear choice and hikers should rush out and buy one. From a marketing perspective, I suspect that is exactly what SPOT wants you to think… and do. But dig a little deeper and you will find technical differences between a PLB and SPOT that should be seriously considered before deciding which unit is best for you.

Disclaimer #1: I am not an engineer so everything that follows is based on my interpretation of the information I found during my research. Please do your own due diligence prior to making your purchase. 

Disclaimer #2: I do not work for ACR Electronics, the manufacturer of the ACR ResQLink, nor was I recruited (remunerated) by ACR Electronics to write (for writing) this article.

Okay… here we go.

Making Waves

Both units transmit their signal in the Ultra High Frequency (UHF) range, which is a range set by the International Telecommunication Union that governs the transmission of electromagnetic waves within the 300MHz to 3GHz range… or to keep it apples-to-apples, from 300MHz to 3,000MHz.

Among other things, an electromagnetic wave has a given (wave) length based on its frequency. The higher the frequency, the shorter the wavelength. The lower the frequency, the longer the wavelength.


Frequency and Wavelength

Frequency and Wavelength

Why is wavelength important? Because, among other things, wavelength determines transmission distance and penetrating power of the signal. In general, longer wavelengths travel farther and have more penetrating power than shorter wavelengths.

The ACR ResQLink transmits at 406MHz, which is at the lower end of the UHF spectrum, and has a wavelength a little less than 2.46 feet (75 centimeters). The SPOT transmits at 1,600 MHz, which is in the middle of the UHF spectrum, and has a wavelength of 0.62 feet (18.8 centimeters).

Bottom Line: The ACR ResQLink’s lower-frequency wavelength is almost four times longer than SPOT’s higher-frequency wavelength. Not only that, but the 406 MHz frequency used by the ACR ResQlink is an internationally recognized, satellite-based, search-and-rescue, distress-alert frequency.


I Got No Power

Wavelength is not all that determines the distance a signal will travel. Signal power also determines distance. Both the ACR ResQLink and SPOT transmit at a given power and that power is measured in watts. Since electromagnetic waves are subject to the laws of physics, every obstacle the signal encounters on its journey to the satellite (tree cover, cloud cover, rain, snow, etc.) weakens the signal. Therefore, stronger power at the source will give the signal more momentum, allow it to lose some power as it negotiates obstacles, and still retain enough signal strength to arrive at the receiving satellite.

The ACR ResQLink transmits at 5 watts. The SPOT transmits at 0.5 watts.

Bottom Line: The ACR ResQLink transmission is 10 times more powerful than SPOT’s transmission.


My Antenna is Longer Than Your Antenna

The ACR ResQLink’s antenna is 10.5 inches long, protects the activation button when wrapped around the unit, and is designed to be deployed, and the unit activated, using only one hand. The SPOT’s antenna is underneath the cover plate and doesn’t have to be deployed, so I assume it is much shorter.

Does it matter?

The National Forest Service did a study on SPOT. They determined the SPOT unit must be oriented with the front cover facing skyward for best results. Otherwise, satellite connection may be impaired or even lost. Given the shape of a SPOT unit, that means you would have to carry it laying flat on top of your shoulder or laying flat on top of your pack. However, if you are not paying for continuous GPS tracking and are only using it as a pseudo-PLB, how you carry it may not be an issue, as long you orient it properly during messaging and for activation.

Bottom Line: Your best judgement.


My Satellite Network and Rescue Protocol Is More Sophisticated Than Your Satellite Network and Rescue Protocol

The ACR ResQLink interacts with the Cospas-Sarsat satellite system and must be registered with NOAA. Once registered, NOAA will send you a sticker (with your registration information) that must be placed on the unit. It is against the law to use a PLB without first registering the device. Once a PLB is activated, a military-like response protocol is set in motion. Other than replacing the batteries (see below), there are no subscription or recurring fees of any kind.





From NOAA:

“Cospas-Sarsat is an international, humanitarian search and rescue system that uses satellites to detect and locate emergency beacons carried by ships, aircraft, or individuals. The system consists of a network of satellites, ground stations, mission control centers, and rescue coordination centers.”

“When an emergency beacon is activated, the signal is received by a satellite and relayed to the nearest available ground station. The ground station, called a Local User Terminal, processes the signal and calculates the position from which it originated. This position is transmitted to a mission control center where it is joined with identification data and other information on that beacon. The mission control center then transmits an alert message to the appropriate rescue coordination center based on the geographic location of the beacon. If the location of the beacon is in another country’s area of responsibility, then the alert is transmitted to that country’s mission control center.”

From what I have read, the Cospas-Sarsat satellite orbits are such that once you activate the ACR ResQLink, a Cospas-Sarsat satellite will receive that signal almost instantly and the search-and-rescue team responsible for your location can be notified in as little as five minutes.

A Cospas-Sarsat satellite does not require both the PLB and the ground station to be in simultaneous contact in order to receive the distress signal. The satellite can receive and store the distress signal and pass it on when the ground station comes into contact.

Plus, the Cospas-Sarsat system in the US is monitored by NOAA and the United States Air Force and they are known to interact effectively with search-and-rescue operations.

SPOT interacts with the commercial, GEOS satellite system by way of contract with GEOS Alliance. Registration with NOAA is not available, but activation/registratiopn with SPOT is required for the unit to work. Activation is accomplished by purchasing a basic service plan, paid annually. There are add-on service plans available that can cost you an additional $13-50 each, paid annually. Once the SPOT SOS signal is activated, a response protocol determined by SPOT and GEOS Alliance is set in motion (see their escape clause, below).

Spot GEOS Satellite Network

Spot GEOS Satellite Network

From SPOT:

  • GPS satellites provide signals
  • SPOT messenger’s onboard GPS chip determines your GPS location and sends your location and preselected message to communication satellites
  • Communication satellites relay your message to specific satellite antennas around the world
  • Satellite antennas and a global network route your location and message to the appropriate network
  • Your location and messages are delivered according to your instructions via email, text message, or emergency notification to the GEOS Rescue Coordination Center

As I understand, the GEOS command center is located in Houston, Texas and a GEOS satellite must have both the SPOT transmitter and the command center in simultaneous contact in order to relay the distress signal. I have also read that with the GEOS satellite orbits, it can take as long as 45 minutes for messages and/or a distress signal to be sent.

Also, from what I have read, the GEOS command center has a reputation of not interacting well with search-and-rescue operations. In fact, in the SPOT Terms and Conditions agreement, they have an escape clause which specifically states, “Should GEOS have reasonable cause to believe that an emergency condition does not exist, GEOS reserves the right to solely contact the primary and secondary contacts identified by you.”

Let me see if I’ve got that right: So if I hit the SOS button on my SPOT, rather than assume I am having a real, life-threatening emergency and then automatically and unquestionably alert search-and-rescue on my behalf, the employees of GEOS Alliance, who have absolutely no idea of my situation or why I sent an SOS, are allowed to determine whether they believe I am having a real emergency… or not…  and whether they will contact search-and-rescue for me… or not? Excuse me!!!!! What the…

Hang tight, I will give you a SPOT Reality Check at the end of this article where the GEOS Alliance decided not to alert search-and-rescue after an SOS signal was received with tragic consequences.

As far as I am concerned, the escape clause in SPOT’s Terms and Conditions is reason enough to avoid SPOT.

Bottom Line: Yes, IMO, the satellite network and rescue protocol used by the ACR ResQLink is far superior to SPOT’s.


Other Points To Consider

GPS Information

Both units transmit GPS location information along with the distress signal. However, if, for some reason, the GPS information can not be transmitted, it is my understanding that Cospas-Sarsat can use something similar to triangulation to determine your location. GEOS has no such capability; however, if you are paying for continuous tracking, GEOS would have your last known GPS location. This “last known location” is also part of the SPOT Reality Check at the end of this post.

Bottom Line: Even


Battery Life and Replacement

The ACR ResQLink uses primary lithium batteries. Once activated, the ACR ResQLink can transmit a distress signal and a homing signal for 24 hours.

The ACR ResQLink’s batteries must be replaced every five years or after each emergency use. Unfortunately, the batteries are deemed not to be user-replaceable. This is a major negative to owning an ACR ResQLink because the manufacturer insists you send the unit to an authorized service center for battery replacement. The service center also inspects and tests the unit to make certain it will last another five years.

So you have to live without your PLB for how ever long it takes to get the unit back from the service center and, from what I’ve read, they will charge you a whopping $150 for the pleasure of doing business with them. If that amount is correct, I think that is an outrageous amount of money to pay for a new battery and for testing the unit. Plus, you have to pay for shipping and insurance, too. Oh, well, it is what it is. 😦

I have no doubt that someone in cyber-ville will find a way to put new batteries in their ACR ResQLink on their own and for a fraction of the cost. And when they do, I expect they will post the procedure online. I hope that happens before I need new batteries… after four more years… or after one rescue.

To their credit, SPOT uses typical AAA batteries. Once the SOS is activated, and with fully charged batteries, SPOT can transmit a distress signal for six days (with clear view of sky and proper orientation) and for three days (with 50% view of sky). The longer transmission time is due to SPOT’s low power rating (see I Got No Power, above). Another thing to keep in mind: If you are paying for continuous GPS tracking and/or you are sending OK messages, your battery life, and thus your distress signal transmission time, will be negatively impacted, so it would be wise to carry extra batteries.

Bottom Line: SPOT’s use of AAA batteries is much a better deal for the consumer… with the above caveat.


Update: December, 2017

Well, that someone in cyber-ville turned out to be… me! 🙂 Yes, I am at the five-year mark and my ACR ResQLink PLB will need a new battery pack by Spring of 2018. I have opened my unit and figured out the battery thing. I am now looking at spot welders, along with all the other gear required to make my own battery pack. Unless something changes, I should be operational and have a new battery pack installed by March, 2018. When I get to that point, I might as well sell battery packs to others who own an ACR ResQLink, as well. And I can tell you this: I will charge a fair price, as low a price as I possibly can, maybe as little as a third of what ACR charges, so other ACR ResQLink owners don’t have to pay that outrageous $150 to get a new battery pack. And the battery pack will use high-quality Panasonic Lithium batteries, the very same batteries that are in my unit right now. So stay tuned. I will post updates here on my blog when I get to that point.


Update: January, 2018

This PLB has three, 3 volt, Panasonic CR123A, primary (single use, non-rechargeable) lithium manganese dioxide batteries wired in series. Pulled the shrink wrap off the battery pack and one of the batteries in my unit is clearly stamped as being good until February, 2022. Not sure about the other two because, the way the batteries are glued together, I can’t see those dates. These batteries are supposed to have a 10 year shelf life, which suggests a manufacture date of February, 2012. ACR says you have to replace the batteries six years after manufacture date… or five years after install. Is that just a CYA recommendation, or did they mix batteries with different dates, or am I missing something?

The only time my PLB has been used is the one test I do at the beginning of each Spring, but that only lasts a few seconds. It doesn’t seem like that annual test, which does light up the strobe a few times, is enough to reduce the life of 10 year batteries by almost half. Plus, a PLB should have zero drain at idle, so why does ACR recommend replacing 10 year batteries five years after install? And other than the annual test, self-discharge would be the only other area of possible concern, but primary lithium batteries only have a self-discharge rate of less than 1% per month. Since I have no knowledge about anything electrical, it’s all a bit perplexing.

I did check the individual cells of my battery pack with a simple battery tester and all three cells showed good (half way into the green). Unfortunately, that doesn’t really give you an indication of remaining battery life. In fact, from what I’ve read so far, the internal chemistry differences of primary lithium batteries makes it difficult, if not impossible, to accurately determine remaining battery life. For the time being, I will continue to use this battery pack while I do more research on primary lithium batteries.



Homing Signal

In addition to a distress signal, the ACR ResQLink transmits a low-frequency homing signal at 121.5 MHz. SPOT does not transmit a homing signal.

Bottom Line: The ACR ResQLink gets a minor nod (for hiking only) because the search-and-rescue team must have the equipment to home in on the signal. In hiking, for the most part, search-and-rescue comes in on foot and I have never heard of a search-and-rescue ground team that carries the equipment needed to home in on this type of signal.


Weight and Form Factor

The ACR ResQLink comes in two flavors: One floats. One doesn’t float. Both have waterproof housings.

ACR ResQLink

ACR ResQLink

The one that floats (above, right) is 1.6 x 1.9 x 4.5” (4.1 x 4.8 x 11.4 cm) and weighs 5.4 oz (153 g)

The one that doesn’t float (above, left) is 1.3 x 1.9 x 3.9” (3.3 x 4.8 x 9.9 cm) and weighs 4.6 oz (130 g)

As a hiker, I really don’t need a PLB that floats. However, after thinking about how I wanted to carry my PLB, I bought the one that floats because it has two slots, one at the top and one at the bottom, and comes with a Velcro strap. This allows me to hang the unit from the left shoulder strap of my pack, which I find preferable to putting the unit in some type of zippered case or carrying it in my pocket. Plus, if I were to have a serious accident, I want the unit to be easily accessible so I can reach it and activate it with only one hand. I don’t want to be lying there hurt and have to fumble around trying to get the unit out of a zippered case or my pocket and then maybe dropping it where it’s impossible for me to retrieve.

ACR ResQLink on Shoulder Strap

ACR ResQLink on Shoulder Strap (this is the one that floats ~ note the slots top/bottom)

The SPOT Messenger is 3.7″ x 2.6″ x 1″ (9.4 cm x 6.6 cm x 2.5 cm) and weighs 5.2 oz (147.4 g).

SPOT Messenger Locator Beacon and Messaging Device

SPOT Messenger Locator Beacon and Messaging Device

ASCHG hike leaders (or van drivers) are required to carry a SPOT Messenger (that belongs to the center) on our hikes so they can send arrival/departure messages back to the center. That way, the person in charge of the center doesn’t get all stressed out if we’re going to be a little late getting back.

Okay… okay… I can understand that logic. However, I have told a couple of people that, in my opinion, someone on each hike should be carrying an ACR ResQLink, as well, because, in my estimation, a personal locator beacon is more dependable in an emergency. I mean, I can’t go on every single hike! 😉 I have convinced at least one hike leader and he now owns an ACR ResQLink, and two other hikers (one is also a hike leader) are also considering the purchase of an ACR ResQLink for themselves.

NOTE: One hike leader who carries a SPOT has told me that, whenever he gets under tree cover, his SPOT loses its satellite connection and stops working, and he has to wait until he gets back out in the open before it starts working again.

Bottom Line: Of the three, the ACR ResQLink that doesn’t float is the lightest. The weights of the other two are about the same. However, the ACR ResQLinks have a smaller form factor, which I prefer, since it is hanging from my shoulder strap.


So What’s A Hiker/Backpacker To Do?

From my perspective, the deeper you venture into the wilderness, the more remote that wilderness is, and the longer you stay, the more you should consider buying a personal locator beacon, especially if you tend to hike solo.

I am mainly a day hiker, but I have done some backpacking and I am gearing up to do more. Anything can happen in the wilderness that might constitute a life-or-death situation for you or someone in your hiking group, even on simple day hikes. Should that happen, and self-rescue or group-rescue is impossible, what would you do?

I would never rely on cell phones working in the back country, so if there is an emergency that requires rescue, without a personal locator beacon, someone would have to hike out and get help. That “hike out” prospect, along with the time it would take to return with help, is what should get your attention because, in a  life-or-death situation, time can be the critical factor in determining whether a person (or the entire group) lives or dies. And if you hike solo… well, for me, the decision to buy a personal locator beacon was a no-brainer.


Which Unit Is Best For You?

Now you’re on your own!

However, when I go into the wilderness, I want to get away from the city and from people. Other than leaving my itinerary with someone I trust, along with instructions on what to do if I’m overdue, I don’t want people tracking my every move on some map. And I don’t want to send “Okay” messages at regular intervals. I want to be left alone to enjoy the wilderness! That’s why I went out there in the first place. 🙂

You may be different. Your family may insist you send “Okay” messages at regular intervals. You may even want to send “Okay” messages at regular intervals. Your family may want to track your progress on a map. You may even want them to track your progress on a map. So make a decision that falls within your comfort zone and the comfort zone of your family — but only AFTER you carefully consider ALL the pros and cons of each unit.


Which Unit Should You Count On In A Life-or-Death Emergency?

Now we’re getting to the meat of the matter. Based on my research, when it comes to a life-threatening emergency in the wilderness where rescue is required and time is of the essence, the ACR ResQLink’s distress signal has the best chance of getting through in the shortest amount of time and in a variety of environmental conditions. Once received, that distress signal will be handled by the best, proven rescue protocol in the country. And that timeliness and rescue protocol will give you your best chance for the shortest signal-to-rescue time possible.

In deciding, keep this is mind:

When it comes to rescue beacons, you want a HIGH power, LOWER-frequency device. A real PLB, such as the ACR ResQLink, is just such a device.

On the other hand, a SPOT is a LOW power, HIGHER-frequency device, which is exactly the opposite of what you want in a rescue beacon.

In closing, let me drive home the message of this article with a SPOT Reality Check, and then I will leave you to your thoughts.


A SPOT Reality Check

April 28, 2012

Yacht Race from Newport Beach, California to Ensenada, Baja California

The Aegean entry had four crew members aboard.

The skipper of the boat had a SPOT and GPS Tracking was enabled.

The SPOT’s SOS distress signal was activated around 1:30 AM.

GEOS Alliance received the Aegean‘s distress signal but made no attempt to contact the Coast Guard even though the Aegean‘s GPS tracking data clearly showed they were in trouble.

The Aegean apparently grounded on rugged North Coronado Island in the middle of the night.

All four crew members died.

Click here to read the article on the Aegean disaster (source of the above information) at Practical Sailor Magazine