EPIRBs, PLBs, and Safety Electronics
These devices are the difference between a search that finds you in hours and one that doesn't find you at all — registration, maintenance, and proper deployment are non-negotiable.
EPIRBs — How 406 MHz Saves Lives
An Emergency Position Indicating Radio Beacon (EPIRB) is a self-contained distress transmitter that, when activated, broadcasts a coded signal on 406 MHz to the COSPAS-SARSAT satellite system — a global network of satellites and ground stations operated cooperatively by the United States, Russia, Canada, and France specifically to detect and locate distress signals. The satellite system receives your EPIRB signal, determines your position (from the beacon's built-in GPS or from satellite Doppler calculations), decodes your unique beacon ID, looks up your registration to determine the vessel name, type, and emergency contact, and relays all of this to the nearest Rescue Coordination Center (RCC). From activation to RCC notification typically takes 5-15 minutes with a GPS-equipped EPIRB.
Modern EPIRBs are GPS-equipped, and this matters enormously. An EPIRB without GPS relies on the COSPAS-SARSAT satellites to calculate position from Doppler shift — a process that can take 45-90 minutes and may produce an initial position accuracy of only 3-5 kilometers. A GPS-equipped EPIRB encodes your exact coordinates into the first transmission, giving the RCC your position within 100 meters in minutes. Every EPIRB sold today includes GPS; if you have an older non-GPS EPIRB, replace it immediately. The difference in rescue time between a GPS-equipped and non-GPS beacon can be measured in hours — hours that matter in cold water, in a sinking vessel, or in deteriorating weather.
Category I EPIRBs are housed in a hydrostatic release bracket that activates automatically if the vessel sinks. The bracket's hydrostatic release unit (HRU) fires at a depth of approximately 1.5-4 meters, freeing the EPIRB from its cradle. The beacon then floats to the surface, activates automatically on contact with water, and begins transmitting. Category II EPIRBs must be manually deployed — you grab the beacon from its bracket, deploy it into the water, and activate it by hand. Category I is the correct choice for any vessel that sails offshore, because if the vessel sinks suddenly (collision, structural failure, knock-down and flood), the crew may not have time to manually activate the EPIRB. The HRU is a consumable component — it has an expiration date stamped on it and must be replaced before that date, typically every 2 years.
Registration is legally required and absolutely critical. In the US, register your EPIRB at beaconregistration.noaa.gov — it is free and takes 10 minutes. You enter the beacon's 15-character Unique Identifier Number (UIN), your vessel's name and description, the number of persons typically aboard, emergency contact information, and your vessel's typical operating area. When the RCC receives your distress alert, the first thing they do is pull up your registration. If the beacon is unregistered, the RCC has no idea what vessel is in distress, what it looks like, how many people are aboard, or who to call to verify the alert. This delays the response by the time it takes to investigate — time you may not have.
Update your EPIRB registration whenever anything changes — new emergency contact phone number, new vessel name, change in typical operating area, change in the number of persons aboard. The registration database is the RCC's first source of information about your emergency. Outdated information slows the response. Set a calendar reminder to review your registration every year, even if nothing has changed, just to confirm the data is current.
An EPIRB's hydrostatic release unit (HRU) has an expiration date — typically 2 years from manufacture. After that date, the HRU may not fire reliably. Check the date stamped on the HRU at the beginning of every sailing season. Replacement HRUs cost $25-40 and take five minutes to install. A $30 part that does not fire when your boat sinks makes your $400 EPIRB worthless.
PLBs vs EPIRBs — Choosing the Right Beacon
A Personal Locator Beacon (PLB) transmits the same 406 MHz signal to the same COSPAS-SARSAT satellites as an EPIRB, but it is a personal device rather than a vessel device. It is smaller (fits in a PFD pocket or clips to a harness), lighter (typically 4-7 ounces), and registered to a person rather than a vessel. A PLB is activated manually — you deploy the antenna, press the button, and hold it above water while it transmits. There is no hydrostatic release, no automatic activation, and no float-free capability. You must be conscious, have the PLB accessible, and operate it yourself.
The key differences between PLBs and EPIRBs come down to battery life, power output, and intended use. An EPIRB transmits at 5 watts on 406 MHz and has a battery rated for 48 hours minimum of continuous operation. A PLB transmits at 5 watts on 406 MHz but has a smaller battery rated for only 24 hours minimum. Both include a 121.5 MHz homing signal that rescue aircraft and vessels can track for the final approach, and both include GPS for position encoding. The EPIRB's longer battery life and float-free/automatic activation make it the right choice as the vessel's primary distress beacon. The PLB's portability makes it the right choice as a personal backup carried by each crew member.
Use cases clarify the distinction. An EPIRB stays with the vessel — it is mounted in a bracket on deck or in the cockpit, and it activates when the vessel is in distress. It floats upright and transmits whether or not anyone is there to operate it. A PLB goes with the person — it is carried in a PFD, clipped to foul weather gear, or stowed in a ditch bag. If a crew member falls overboard, their PLB activates a distress alert specific to that person. If the vessel sinks and the crew is in a life raft without the EPIRB, someone's PLB can still summon rescue. If you are hiking on a remote island and break your leg, the PLB works ashore too — it is not limited to maritime use.
The recommended approach for offshore sailing is: one Category I EPIRB per vessel mounted in a hydrostatic release bracket, plus one PLB per person for crew members on offshore passages. The EPIRB is the automatic, high-endurance distress beacon that works even if the crew is incapacitated. The PLBs are personal backup devices that cover the scenarios the EPIRB cannot — overboard crew, separation from the vessel, and situations where the EPIRB was not deployed or was lost. PLBs cost $250-350 and have no subscription fees. When spread across the life-or-death scenarios they cover, this is among the most rational safety investments on the boat.
Register your PLB at beaconregistration.noaa.gov just like an EPIRB, but note that PLBs are registered to a person, not a vessel. Include the vessel name in the additional information field, and list a shore-based emergency contact. If you lend your PLB to crew for a passage, update the registration with their information — the RCC needs to know who activated the beacon, not who bought it three years ago.
SART, AIS-SART, and the DSC Distress Button
Beyond EPIRBs and PLBs, three additional electronic systems play critical roles in the distress communication chain: radar SARTs, AIS-SARTs, and the DSC distress button on your VHF radio. Each serves a different purpose in the rescue process and targets a different stage — from initial detection by rescuers to final homing for the approach. Understanding what each does, and equally what each does not do, prevents the dangerous assumption that activating one device has you fully covered.
A SART (Search and Rescue Transponder) is a radar-triggered device. When a searching vessel's radar signal hits the SART, it responds with a burst of radar pulses that appear on the rescuer's radar screen as a distinctive line of 12 dots radiating outward from the SART's position. This makes the SART visible on radar from 8-10 nautical miles — far beyond the visual detection range of a life raft. The traditional radar SART operates on the 9 GHz (X-band) frequency. However, many modern vessels now use S-band (3 GHz) radar or solid-state radar that may not trigger a 9 GHz SART reliably. This is why the AIS-SART has emerged as a preferred alternative.
An AIS-SART transmits an AIS signal rather than a radar response. When activated, it broadcasts a special AIS message that appears on every AIS display within VHF range — typically 5-10 nautical miles depending on antenna height — as a distinctive concentric circle symbol with the SART's GPS position. The AIS-SART does not require the searching vessel to have radar; any vessel with an AIS display (which is most commercial and many recreational vessels) will see it. AIS-SARTs are smaller, lighter, and cheaper than radar SARTs, and they provide GPS-accurate position data. The limitation is range — VHF line-of-sight from a device floating at water level limits detection to vessels within about 5-10 miles.
The DSC distress button on your VHF radio is often the fastest distress alert available because it reaches nearby vessels and Coast Guard stations instantly on Channel 70. When you press and hold the red button (lifting the spring-loaded cover first), the radio transmits a DSC distress message containing your MMSI, GPS position, nature of distress (if you had time to select one), and time of transmission. Every DSC-equipped radio and Coast Guard station within VHF range receives the alert with your position plotted on their screen. This should be your first distress action in most scenarios because it reaches the vessels closest to you — the vessels that can respond fastest. Follow the DSC alert immediately with a voice Mayday on Channel 16 to provide details that the digital message cannot convey.
A DSC distress alert without a GPS position is dramatically less useful — the Coast Guard receives your MMSI and the fact that you are in distress, but not where you are. Verify that your VHF radio is receiving GPS data by checking the display for a position readout. If the GPS connection has failed and you need to send a DSC distress alert, manually enter your position from your chartplotter or handheld GPS before pressing the distress button, if time permits.
MOB Electronics — AIS Beacons, Smart Wearables, and Recovery Systems
Man overboard (MOB) electronics address the terrifying reality that a person in the water is nearly impossible to see from a sailboat, especially at night, in waves, or in poor visibility. Traditional MOB recovery relies on the helmsperson seeing the person go over, immediately marking the GPS position, executing a recovery maneuver, and visually reacquiring the person — a chain that breaks if any single link fails. MOB electronics add redundancy by providing automatic alerts, GPS position marking, and electronic homing signals that do not depend on someone witnessing the fall.
AIS MOB beacons (Ocean Signal rescueME MOB1, ACR AISLink, Kannad SafeLink R10) are personal transponders that clip to a PFD or life jacket and activate on water contact or manual deployment. When triggered, they broadcast an AIS MOB message that appears on every AIS display within 5-7 miles, including your own chartplotter, as a distinctive MOB symbol with GPS coordinates. Simultaneously, they transmit a 121.5 MHz homing signal that rescue vessels can track with a direction-finding receiver for the final approach. The AIS signal provides the initial alert and approximate position; the 121.5 MHz signal guides the final recovery. Battery life is typically 24 hours — long enough for a search even if immediate recovery fails.
Smart wearables represent the newest category of MOB technology. Devices like the OLAS (Overboard Location Alert System) use Bluetooth tags worn by each crew member that communicate with a base station (usually a phone or tablet running the OLAS app). If a tag moves out of Bluetooth range (approximately 20-30 meters), the base station triggers an immediate audible alarm and GPS waypoint. The advantage is speed — the alert occurs within 8-15 seconds of the person going overboard, before they have drifted far. The limitation is that Bluetooth range is short and the system depends on the phone/tablet being powered on and running the app. OLAS works best as an early warning system that complements, not replaces, an AIS MOB beacon.
The recommended MOB electronics stack for offshore sailing is: an OLAS Bluetooth system for instant fall detection and alerting, plus an AIS MOB beacon per crew member for long-range electronic location after the fall. The OLAS detects the fall immediately and alerts the crew aboard; the AIS MOB beacon provides a persistent, long-range signal that guides recovery even if initial visual contact is lost. Add to this a personal PLB as the ultimate backup that summons COSPAS-SARSAT rescue if the vessel cannot recover the person. This three-layer approach — immediate detection, local homing, global rescue — covers the full range of MOB scenarios from the benign (fell off the swim ladder in calm water) to the catastrophic (swept overboard at night in heavy weather with an incapacitated crew).
Test your MOB electronics at the dock, in daylight, with the crew assembled. Activate an AIS MOB beacon and verify it appears on your chartplotter. Trigger the OLAS system by walking a tag out of range and verify the alarm sounds. Walk through the MOB procedure: who takes the helm, who marks the GPS position, who calls on VHF, who prepares recovery gear. The first time you use this equipment should not be the first time someone is in the water.
Battery Replacement, Testing, and Maintenance Schedules
Every safety electronic device depends on a battery that degrades over time, whether the device has been used or not. EPIRBs, PLBs, SARTs, AIS-SARTs, and MOB beacons all have battery expiration dates stamped on the device or documented in the manual, and these dates are absolute deadlines, not suggestions. A distress beacon with an expired battery may still transmit — or it may transmit at reduced power, for reduced duration, or not at all. The COSPAS-SARSAT system specification requires EPIRBs to transmit for a minimum of 48 hours; an expired battery may fail after 12 hours, before search assets reach your position.
EPIRB batteries typically have a 10-year shelf life from manufacture and must be replaced by the expiration date. Replacement is a factory or authorized service center operation — you send the EPIRB to the manufacturer, they replace the battery, test the unit, and return it recertified. Cost is $200-350 depending on manufacturer and model. The hydrostatic release unit (HRU) has a separate, shorter expiration — typically 2 years — and can be replaced by the owner with a simple swap of the HRU cartridge on the mounting bracket. PLB batteries have a 5-7 year life depending on model, and some PLBs are not user-serviceable — the entire unit may need to be replaced when the battery expires.
Testing is required and straightforward. EPIRBs have a self-test function — a button that causes the beacon to emit a brief test transmission at reduced power and confirm GPS lock, battery voltage, and transmitter function via indicator LEDs. Perform this self-test monthly and record the result in your maintenance log. The self-test does not trigger a COSPAS-SARSAT alert. Additionally, NOAA coordinates a SARSAT beacon test protocol — you can perform a full-power test burst during the first 5 minutes of any hour, limited to one second, but in practice the self-test function is sufficient for routine verification.
Maintenance schedule summary: Check EPIRB self-test monthly. Replace EPIRB HRU by its expiration date (every 2 years). Replace EPIRB battery by its expiration date (typically every 10 years or after any deployment). Replace PLB battery by its expiration date (5-7 years). Replace AIS MOB beacon battery per manufacturer schedule (typically 5-7 years). Replace AIS-SART battery per manufacturer schedule. Update EPIRB and PLB registrations annually or whenever any information changes. Inspect mounting brackets, lanyards, and attachment points for corrosion and UV degradation at the start of every season. Keep all receipts and certificates — the Coast Guard and your insurer may ask for proof of current battery and registration status.
Create a safety electronics maintenance spreadsheet listing every device, its serial number, battery expiration date, HRU expiration date (if applicable), registration confirmation number, and last test date. Post a printed copy at the nav station and keep a digital copy in your phone. When battery or HRU replacement dates approach, order the replacements three months early — manufacturer backlogs and shipping delays have left boats sailing with expired equipment because the replacement arrived after departure.
Summary
A GPS-equipped Category I EPIRB in a hydrostatic release bracket is the minimum standard for offshore sailing — it provides automatic activation, 48-hour battery life, and position accuracy within 100 meters via COSPAS-SARSAT.
PLBs complement the vessel's EPIRB by providing personal, portable distress alerting registered to each crew member — carry one per person on offshore passages.
AIS-SARTs are increasingly preferred over radar SARTs because they appear on all AIS displays without requiring the searching vessel to have compatible radar.
The DSC distress button on your VHF radio should be your first distress action in most scenarios — it instantly alerts all DSC-equipped vessels and Coast Guard stations within VHF range with your GPS position.
MOB electronics should be layered: Bluetooth fall detection (OLAS) for immediate alerting, AIS MOB beacons for homing, and PLBs for global rescue activation.
Battery expiration dates on EPIRBs, PLBs, and MOB devices are absolute deadlines — test monthly, replace on schedule, and maintain current registration at beaconregistration.noaa.gov.
Key Terms
- COSPAS-SARSAT
- An international satellite-based search and rescue system that detects and locates 406 MHz distress beacons (EPIRBs, PLBs, ELTs). Operated cooperatively by the US, Russia, Canada, and France, it provides near-global coverage with position notification to rescue centers within minutes.
- Category I EPIRB
- An EPIRB mounted in a hydrostatic release bracket that activates automatically if the vessel sinks to approximately 1.5-4 meters depth. The beacon floats free, surfaces, and begins transmitting without human intervention.
- PLB (Personal Locator Beacon)
- A portable 406 MHz distress beacon registered to a person rather than a vessel. Manually activated, with a 24-hour minimum battery life. Carried in a PFD or on a person as a backup to the vessel's EPIRB.
- AIS-SART
- A Search and Rescue Transponder that broadcasts an AIS signal rather than a radar response. Appears as a distinctive concentric-circle symbol on AIS displays within VHF range, providing GPS-accurate position data for the search vessel.
- Hydrostatic Release Unit (HRU)
- A pressure-activated mechanism on a Category I EPIRB bracket that fires at a water depth of 1.5-4 meters, releasing the EPIRB to float to the surface. HRUs have a 2-year expiration date and must be replaced on schedule.
- 121.5 MHz Homing Signal
- A low-power continuous signal transmitted by EPIRBs, PLBs, and MOB beacons that rescue aircraft and vessels can track with direction-finding equipment for the final approach to the distress position. Does not provide position data — it guides the last miles of the search.