⚠️ Important before buying
An AIS MOB beacon is not an EPIRB/PLB: it alerts vessels within AIS range (a few miles), not satellite-based rescue services. For offshore sailing, you need 406 MHz Cospas-Sarsat (EPIRB or PLB). Confusing the two creates a false sense of offshore security.
In brief
The essentials in 30 seconds
- Three devices NOT to confuse: the PLB (personal beacon, 406 MHz satellite, registered to a person), the EPIRB (vessel beacon, 406 MHz satellite, registered to a boat), and the AIS MOB beacon (man overboard, local AIS only — no satellite).
- The category determines activation: Cat. 1 = automatic float-free release (hydrostatic release unit HRU, sometimes called "zafe"), Cat. 2 = manual activation.
- The key features in 2026: GNSS (fast position), AIS (local detection by nearby vessels), RLS (Galileo acknowledgment), NFC (testing/configuration via the app).
- A beacon that is not coded or registered is a beacon that slows down — or loses — your rescue. This is the issue we handle most often in the workshop.
🛠️ Workshop note
Skysat distributes, codes and provides after-sales service for beacons (Ocean Signal, ACR…) in Carnac. This guide outlines what we would choose for our own boat, program by program.
1. EPIRB, PLB, AIS MOB: three devices, three uses
This is the most dangerous and most common confusion.
- EPIRB (Emergency Position-Indicating Radio Beacon) — the boat's beacon. Transmits on 406 MHz to Cospas-Sarsat satellites (global coverage) + 121.5 MHz for homing. Registered to the vessel. It is the reference distress alert for "the boat is sinking / we are abandoning ship".
- PLB (Personal Locator Beacon) — same principle 406 MHz satellite, but registered to a person, compact, manual activation, no automatic release. Worn on the body. Ideal as a complement, or for those who frequently change boats.
- AIS MOB beacon (man overboard) — note: it does NOT transmit to satellites. It triggers a local AIS alert detected by nearby vessels (typically a few miles) and displays the man overboard on their chartplotter/AIS. Perfect for recovering a crew member who has fallen overboard near the boat; it is not a satellite alerting method.
In short: AIS MOB = recover a crew member now, via nearby vessels. EPIRB/PLB = trigger global rescue via satellite. Both are complementary, not interchangeable.
2. Category 1 vs 2: automatic or manual release
For EPIRBs, the category describes the activation method:
- Category 1 (float-free) — mounted in a cradle with a hydrostatic release unit (HRU) that automatically releases the beacon at ~4 m depth if the boat sinks. The beacon floats and activates on its own. Essential if the scenario "the boat sinks quickly, crew incapacitated" is plausible (offshore, passage-making, reduced crew).
- Category 2 (manual) — fixed in an indoor mount; a human must grab and activate it. Less expensive, ideal for coastal sailing where you have control, but useless if no one can reach it.
With Ocean Signal, the EPIRB3 is Cat. 2 (manual) and the EPIRB3 Pro is Cat. 1 (float-free) — this is the main difference between the two, beyond the price.
3. GNSS, AIS, RLS, NFC: the key features
Modern 406 MHz beacons are not all equal. What truly changes the speed and reliability of rescue:
GNSS
Precise position, quickly
The beacon transmits its precise position within the first minutes, instead of leaving the satellites to triangulate. Non-negotiable today.
AIS
Local detection
In addition to 406 MHz satellite transmission, the beacon appears on the AIS of nearby vessels: a cargo ship or neighboring mooring vessel can locate you even before official resources arrive.
RLS
Acknowledgment
Via Galileo, an acknowledgment: an LED confirms that your alert has been received and located. Psychologically huge when you're waiting alone in survival mode.
NFC
Test & monitoring
Test and configuration via smartphone app (check self-test, read history). Useful for monitoring.
In terms of battery life: a minimum of 24 hours of transmission at -20 °C, with "Pro" models aiming for 48 hours. The battery has a lifespan (often 7 to 10 years) that must be respected (see §5).
The EPIRB3 / PLB3 Ocean Signal models combine AIS + RLS + NFC; the EPIRB1 / PLB1 are the 406 + GNSS "essential" versions, without AIS.
4. Coding and registration: the costly trap
This is the issue we resolve most often in the workshop — and the one that online "cheapest" purchases overlook.
A 406 MHz beacon is only operational once it has been coded and then registered. In France, three links:
- MMSI + vessel station license — ANFR. If the boat is equipped with VHF/DSC, the MMSI (9 digits) and the vessel station license are obtained from the ANFR, online at maritime.anfr.fr. The license — to be kept on board — lists the MMSI and the reference of each declared beacon.
- Beacon coding. Programming with the French country code + the identifier (the MMSI for a maritime EPIRB, or a serial number). A beacon purchased abroad is often coded for another country → the alert would go to the wrong coordination center. Skysat recodes for France (70 € HT flat rate).
- Registration — mandatory and free. Declaration of the beacon in the national registry of 406 MHz beacons, operated by CNES (FMCC France): registre406.cnes.fr. Here, you associate your emergency contacts: this is what enables rescue services to identify you — the vast majority of alerts are false alarms, which a call to emergency contacts can resolve without mobilizing resources. This is a regulatory requirement under Division 175 of the vessel safety regulations.
Resale / change of boat: a beacon that changes hands must be re-registered; we regularly see beacons that still point to the previous owner.
Buying the beacon is just the beginning. Coding + license + registration = what makes it truly operational — and this is precisely where an installer saves you time (and perhaps more).
5. Maintenance: battery, hydrostatic release, overhaul
A beacon must be maintained — otherwise it won't activate when needed:
- Battery — typical lifespan 7 to 10 years; beyond that, mandatory replacement (flat rate EPIRB1 battery replacement: 233 € HT at our workshop). Regular self-test (TEST button / NFC app) does not replace the battery expiry date.
- Hydrostatic release unit (HRU) for Cat. 1 — a perishable part (typically every 2 years): after the expiry date, automatic release is no longer guaranteed.
- Shore-Based Maintenance (SBM) — for beacons that require it, flat rate Shore-Based Maintenance from 230 € HT. We also handle the overhaul of certain beacons (e.g., Kannad).
In short: a beacon has an expiry date, like a life raft. Check the battery and hydrostatic release unit during the boat's annual overhaul — this is the habit that avoids a nasty surprise when it matters.
6. Comparison chart
| Criteria | PLB1 | PLB3 | EPIRB1 Cat. 2 | EPIRB3 Cat. 2 | EPIRB3 Pro Cat. 1 |
|---|---|---|---|---|---|
| Type | personal | personal | vessel | vessel | vessel |
| 406 MHz satellite | ✓ | ✓ | ✓ | ✓ | ✓ |
| Integrated GNSS | ✓ | ✓ | ✓ | ✓ | ✓ |
| AIS | — | ✓ | — | ✓ | ✓ |
| RLS (Galileo) | — | ✓ | — | ✓ | ✓ |
| NFC (app) | — | ✓ | — | ✓ | ✓ |
| Activation | manual (on person) | manual (on person) | manual | manual | auto float-free |
| Transmission range | ≥24 h | ≥24 h | ≥48 h | ≥48 h | ≥48 h |
| Battery lifespan | 7 years | 7 years | ~10 years | ~10 years | 10 years |
| 2026 HT price | 345 $ | 570 $ | 499 $ | 810 $ | 945 $ |
Prices HT — Skysat catalog (Odoo), June 2026. Other references in the catalog: ACR GlobalFIX V5 Cat. 2 (835 $), AIS MOB1 / MOB2 beacons (307 $ / 387 $), AIS SART safeSEA S200 (750 $ — the AIS-SART is used to be located from a liferaft, yet another function), ready-to-go safety kits. France coding 70 $. See also the satellite communication comparison.
7. 5 workshop traps
Trap #1
Confusing AIS MOB with EPIRB/PLB.
The #1 trap. An AIS MOB beacon works locally (AIS); for offshore rescue, you need 406 MHz.
Trap #2
Buying a beacon coded for another country.
Common with purchases abroad: the alert goes to the wrong center. Must be recoded before the first departure.
Trap #3
Never registering (or not updating).
An unregistered beacon deprives rescue services of your details. On resale/change of boat: re-register.
Trap #4
Choosing Cat. 2 when the program requires float-free.
Offshore or reduced crew: if no one can grab the beacon, only a Cat. 1 will activate on its own.
Trap #5
Forgetting expiry dates.
Battery (7-10 years) and hydrostatic release unit (HRU) (expiry ~2 years): a beacon that "looks new" can be out of service. Self-test does not replace the calendar.
8. Which beacon for which program
- Coastal / day sails, where you have control → EPIRB1 Cat. 2 (499 $) or EPIRB3 Cat. 2 (810 $) if you want AIS + RLS. A PLB1 (345 $) as a complement on the skipper.
- Offshore / passage-making / reduced crew → EPIRB3 Pro Cat. 1 float-free (945 $): it activates on its own if the boat sinks quickly. Plus a PLB3 (570 $) on each watch crew member.
- Regattas, multi-boat programs, or "I want it to follow me" → the PLB3 personal AIS/RLS beacon is the most versatile.
- Man overboard recovery (crew overboard) → an AIS MOB beacon (MOB1/MOB2), in addition to the boat's EPIRB — not instead of.
And the workshop's honest take: the most expensive beacon poorly coded is worth less than a basic EPIRB1 properly registered. The priority budget is the 406 MHz + coding + registration; the rest is comfort (useful, but secondary).
9. FAQ
What's the difference between an EPIRB and a PLB?
The EPIRB is registered to the boat (and can be Cat. 1 with automatic float-free); the PLB is registered to a person, compact, manual activation. Both transmit on 406 MHz to Cospas-Sarsat satellites. Many boats have both.
Is an AIS MOB beacon sufficient for offshore sailing?
No — it only alerts vessels within AIS range (a few miles). For offshore sailing, you need an EPIRB or PLB 406 MHz.
Category 1 or 2?
Cat. 1 = automatic float-free release (the boat sinks, the beacon activates on its own). Cat. 2 = manual activation. Offshore or reduced crew: Cat. 1 is strongly recommended.
What is RLS?
The Return Link Service (via Galileo): an acknowledgment. An LED on the beacon confirms that your alert has been received and located. Available on EPIRB3 / PLB3 models.
Do I need to register my beacon, and is it free?
Yes, it's mandatory. The beacon is registered free of charge in the national registry of 406 MHz beacons (CNES / FMCC France) at registre406.cnes.fr, with your emergency contacts. For a vessel equipped with VHF/DSC, the MMSI and vessel station license come from the ANFR (maritime.anfr.fr). Beacon coding, however, is a technical service — we provide it for 70 $ HT.
How long does the battery last?
Depending on the model, 7 to 10 years. Beyond that, mandatory replacement. On Cat. 1 beacons, the hydrostatic release unit (HRU) must also be replaced periodically (~2 years).
Can I buy a cheaper beacon abroad?
You can, but it will often be coded for another country: you'll need to recode it for France and re-register it, otherwise the alert will go to the wrong coordination center. The "good deal" comes with risk.
Transparency — Skysat distributes, codes and provides after-sales service for Ocean Signal and ACR beacons at the Carnac workshop (Morbihan). The recommendations in this guide are based on our coding, installation and maintenance experience, not on supplier data sheets. When a simpler solution is sufficient for your program, we say so.
