When it comes to personal safety on the water, few choices are as critical—or as confusing—as deciding between a Personal Locator Beacon (PLB) and a Man Overboard Device (MOB). Both are compact, life-saving technologies designed to alert others if you go into the water. But they work in very different ways, and the right option for you depends on where, how, and with whom you boat.
This guide breaks down the pros and cons of each and offers practical advice to help you make the best choice for your boating lifestyle.
What’s the Difference Between a PLB and a MOB?
Let’s start with the basics:
Personal Locator Beacon (PLB):
- Satellite-based emergency beacon using the dedicated 406MHz Distress Frequency
- Sends your GPS location to search and rescue authorities (via COSPAS-SARSAT)
- Works anywhere on the planet, with no reliance on your vessel or crew
- Registration with local rescue authorities is required
AIS Man Overboard Device (MOB):
- Sends a distress signal locally, typically via AIS (Automatic Identification System) and DSC (Digital Selective Calling)
- Alerts nearby vessels, including your own, to your position
- Relies on line-of-sight radio signals and compatible onboard systems
PLB: Pros and Cons
Pros:
- Global coverage—works offshore, in remote areas, or solo
- Transmits distress signal directly to international search and rescue
- Long battery life (often 5–7 years)
- Compact and rugged for long-term use
Cons:
- No automatic alert to your own boat or crew*
- Usually requires manual activation*
🔗 Explore PLBs from ACR Electronics and Ocean Signal.
*The Ocean Signal rescueME PLB3 with AIS is the only combined PLB with AIS and does alert your own boat and crew. It is also semi-automatic and can be activated automatically when the lifejacket inflates.
MOB Device: Pros and Cons
Pros:
- Instant alert to your vessel and nearby boats via AIS and/or DSC
- Can integrate with chartplotters and onboard MOB alarms
- Ideal for crewed boats or races where rapid response is key
- Some activate automatically when inflated with lifejacket
Cons:
- Limited range—line-of-sight only (typically up to 5 NM)
- Doesn’t notify international rescue authorities
- Requires compatible equipment onboard (AIS receiver, DSC VHF, etc.)
🔗 Check out AIS MOB devices from Ocean Signal.
Choosing the Right Device for Your Needs
Here’s a quick decision matrix:
| Your Boating Style | Best Choice | Why |
|---|---|---|
| Solo sailing or long offshore passages | PLB or AIS PLB | Global satellite reach, independent rescue |
| Coastal cruising with crew | MOB Device or AIS PLB | Alerts crew instantly, better for local rescue |
| Ocean racing or regattas | MOB Device + PLB or AIS PLB | MOB for crew response, PLB as backup |
| Kayaking, SUP, or remote fishing | PLB or AIS PLB | Compact, reliable, no vessel dependency |
| Motor yacht with AIS/DCS systems | MOB Device or AIS PLB | Integrates with onboard electronics |
Pro Tip: Why Not Both?
For the highest level of safety, many seasoned sailors and commercial mariners carry both a PLB and an AIS MOB device. The MOB alerts your crew immediately, while the PLB ensures help is on the way—even if no one saw you go in.
If both devices are installed properly within your lifejacket (ideally one semi-automatic activated, one manual), you’ve built a multi-layered safety net.
Better yet, get the combination of both in one small compact beacon that was designed to fit inside your lifejacket. The Ocean Signal rescueME PLB3 with AIS brings the best of both distress beacons in one palm sized Personal Locator Beacon. In North America, check out the ACR ResQLink AIS PLB.
The UML Difference
Your lifejacket is the first line of defense—but it’s the technology inside that can bring the help you need. Whether you choose a PLB, a MOB, or both, the most important thing is making sure the device matches your boating environment and is installed correctly for reliable use.
UML (United Moulders Limited), a key part of the ACR Electronics and Ocean Signal family, offers lifejacket manufacturers a comprehensive, integrated solution for personal flotation device (PFD) safety systems. With decades of expertise in marine safety, UML provides a full range of components—from reliable oral inflation tubes and automatic inflator systems to advanced AIS Personal Locator Beacons and high-intensity lifejacket lights. This all-in-one capability not only streamlines the supply chain for manufacturers but also ensures that every lifejacket produced meets the highest standards of reliability, innovation, and performance—backed by the trusted safety legacy of ACR and Ocean Signal.