Contents: Satellite messengers and PLBs

Personal Locator Beacons
Satellite Messengers

Personal Locator Beacons

The SOS from a ‘PLB’ is the most powerful electronic cry for help you can get. Satellite-based, these are designed to send an SOS from anywhere on earth, no mobile signal required. They are small enough to fit in the palm of your hand. If you want to be able to call the cavalry wherever you are then consider buying a Personal Locator Beacon.

Although satellite messengers like the Garmin inReach units also offer an SOS, these do not transmit as powerfully as a PLB and are less likely to punch through foliage or other signal blocking obstructions. Satellite Messengers can only be located by the GNSS location encoded in the SOS. PLBs offer four location methods.

The SOS from a PLB goes via a tried and tested, international, government-funded SOS satellite system called Cospas-Sarsat. It has been used for decades by boats and planes. If you’ve never heard of a Personal Locator Beacon before, that might be because they only became legal to use on land in the UK in 2012.

A PLBs SOS is picked up by a 24/7/365 operation. The SOS information is quickly passed on to the emergency services in the country that the emergency has occurred. Then a local rescue can be launched. Learn the detail of what happens when you press the SOS button here.

In the UK, the Cospas-Sarsat satellite system will quickly relay any SOS to the Cospas-Sarsat UK Mission Control Centre (UKMCC) in Fareham, Hampshire. The UKMCC is deliberately situated alongside the RAFs Aeronautical Rescue Coordination Centre who can initiate rescues anywhere in the UK.

Any Cospas-Sarsat approved PLB must have a battery that is guaranteed for a minimum of 5 years. When the battery needs changing it must be done by the manufacturers. There are no other costs. The McMurdo FastFind 220 is a good example of these handheld devices and costs around £240. The Ocean Signal PLB1 is small, comes with a 7 year battery life and is another good option.

The SOS from a PLB can be detected in a number of separate and independent ways. When you press the SOS button, the weatherproof beacon will transmit a powerful 406MHz signal for at least 24 hours even if the temperature is minus 20 deg C. The SOS contains your GPS location as PLBs contain a GNSS receiver. If the PLB’s GNSS receiver has broken, then the transmission can still be located by the moving satellites. They get a fix by measuring how the transmission frequency appears to vary with their motion. This location method is called doppler processing. Cospas/Sarsat explain how it’s done.

The PLB also transmits an additional lower power 121.5MHz homing signal that helps helicopters find you when they get within a few kilometres. The beacon flashes a bright strobe light too. This is often spotted before any need to use the homing signal.

You’re legally required to register a PLB using an online form. That records useful information about your contacts and yourself. The SOS transmission includes a unique code which identifies who the PLB belongs to. When the SOS is received your personal information is retrieved and passed on to the rescuers. They will phone your contacts and may call you by your first name when they get to you.

If you want the best possible electronic SOS, then get a Personal Locator Beacon. Check out units by Ocean Signal, ACR and McMurdo.

Satellite messengers

Functionality varies but a good satellite messenger can offer two-way messaging, live tracking and an SOS anywhere in the world. The newer iPhones already incorporate a satellite-based SOS and this tech will likely arrive on Android phones before too long. Good news for outdoors fans.

Garmin call their satellite messaging technology ‘inReach’. The Garmin inReach Mini is a tiny satellite messenger. Garmins larger GNSS mapping units like the inReach Explorer, GPSMap 67i, and Montana 700i all include satellite messaging in the handheld.

These handheld devices can send text messages to email addresses, send SMS texts to mobile phones or text other satellite messengers. These may be just a few outgoing preset messages (SPOT gen 4 and inReach) or could be custom 2-way messaging for proper conversations (inReach)

They use communications satellite constellations to provide the service. The Garmin inReach devices use the Iridium satellite system which offers 100% global coverage. The SPOT devices use the Globalstar system which covers about 80% of the planet. The UK and mainland Europe are covered by both systems.

Satellite messengers have GNSS receivers in them so the messages may be accompanied by an accurate location. They will also transmit live-tracking points so that your progress can be followed in real time online on a personal topo map. They may also record a track to the devices internal memory to download later.

They all have an SOS button that works very similarly to a PLB except that the signal from a satellite messenger is not as powerful as that from a PLB. The frequency it uses is higher and more likely to get blocked by foliage or other difficult conditions. If the PLBs GNSS receiver breaks, the SOS cannot include a GPS location and there is no other way to locate the unit. However, if all is working properly the SOS should work.

SOS buttons on the inReach units (and any other devices that use the Iridium constellation) contact the International Emergency Response Coordination Centre (IERCC). This is like a commercial version of Cospas-Sarsat. It is also a 24hr, 7 days a week, 365 days a year operation. If you do get a satellite messenger, get one that transmits an SOS to GEOS. Not all do. The last time I looked, the Yellowbrick units did not contact the IERCC but a nominated group of contacts. Not so good if they’re all asleep.

As well as the cost of the unit there will be a monthly subscription for the service. These aren’t a cheap option. The popular Garmin inReach Mini cost about £250 to buy and the cheapest ‘Safety’ subscription option is currently £13pcm.

SPOT were the original satellite messengers and Garmin are probably the biggest name today. Other names to check out are Bivystick Blue, Zoleo Satellite Communicator and the Somewhere Global Hotspot. Most send an SOS to the IERCC but offer different functions and subscription options. All require a linked smartphone to provide full functionality.

Although the tiny Garmin inReach Mini (100g) can be conveniently operated with a phone app it will also work as a standalone device. Handy.