406 MHz
Satellite distress frequency (Cospas-Sarsat)
48 hrs
Minimum EPIRB battery life at −20°C
5 years
Typical battery replacement interval
What Is an EPIRB?
An Emergency Position Indicating Radio Beacon (EPIRB) is a vessel-mounted distress transmitter that, when activated, broadcasts a unique 406 MHz digital signal to the Cospas-Sarsat satellite network. The signal is relayed to a Local User Terminal (LUT), processed by a Mission Control Center (MCC), and forwarded to the nearest Rescue Coordination Center (RCC) — typically the U.S. Coast Guard — which dispatches search and rescue assets.
Modern EPIRBs also transmit on 121.5 MHz as a homing signal, allowing SAR aircraft and vessels to home in once they are within range. Most current units include an integrated GPS receiver that encodes the vessel's position directly into the 406 MHz signal, reducing the search area to a circle of approximately 100 meters.
The Cospas-Sarsat system uses both LEO (low-earth orbit) and MEO/GEO (geostationary) satellites. LEO satellites provide the most accurate Doppler-derived position but may take up to 90 minutes for a satellite to pass overhead. GEO satellites provide near-instant alert but with no position until GPS data is included.
How the System Works
EPIRB activates (auto or manual)
406 MHz signal transmitted continuously
Cospas-Sarsat satellite receives signal
Signal relayed to ground station (LUT)
Mission Control Center decodes 15-digit ID
NOAA registration database queried
Coast Guard Rescue Coordination Center alerted
SAR assets dispatched to GPS position
EPIRB vs PLB vs SART
The exam distinguishes between these three devices. Know the key differences cold.
| Feature | EPIRB | PLB | SART |
|---|---|---|---|
| Signal frequency | 406 MHz (satellite) + 121.5 MHz (homing) | 406 MHz (satellite) + 121.5 MHz (homing) | 9 GHz (X-band radar response) |
| Satellite system | Cospas-Sarsat (global) | Cospas-Sarsat (global) | None — radar only |
| Registration | Required — NOAA database | Required — NOAA database | Not required |
| Deployment | Cat I: auto float-free; Cat II: manual | Manual only | Manual — survival craft use |
| Typical battery life | 48 hours minimum (406 MHz) | 24 hours minimum | 96 hours standby / 8 hours transmit |
| Who must carry | Inspected vessels beyond 3 nm | Individual — not a vessel substitute | SOLAS vessels — survival craft |
| Size / portability | Vessel-mounted, larger unit | Personal — worn or pocket-size | Handheld — survival craft use |
| GPS position | Integrated GPS (modern units) | Integrated GPS (most units) | Derived from radar bearing |
Category I vs Category II EPIRBs
Category I
- ▸Auto float-free activation via hydrostatic release unit (HRU)
- ▸Also manually activatable
- ▸Mounted in a float-free bracket on deck
- ▸HRU activates at 1–4 meters depth
- ▸HRU has 2-year expiration (separate from battery)
- ▸Required for inspected vessels on offshore routes
- ▸Activates even if crew is incapacitated or vessel sinks rapidly
Category II
- ▸Manual activation only — no float-free capability
- ▸Stored in a bracket, but bracket does not release automatically
- ▸No hydrostatic release unit required
- ▸Acceptable for some commercial operations and offshore recreational use
- ▸Less expensive than Category I
- ▸Must be manually grabbed and activated in an emergency
- ▸NOT acceptable as the sole EPIRB where Cat I is required
USCG Carriage Requirements
Requirements are governed primarily by 46 CFR 25.26 (uninspected vessels) and the vessel's Certificate of Inspection (COI) for inspected vessels.
| Vessel Type | Operating Area | Required? | Category |
|---|---|---|---|
| Uninspected recreational vessel | Within 3 nm | Not required (recommended) | — |
| Uninspected recreational vessel | Beyond 3 nm | Not federally required (strongly recommended) | — |
| Uninspected commercial vessel (< 100 GT) | Beyond 3 nm, domestic | Required | Cat I or Cat II |
| Inspected vessel — passengers for hire | Beyond 3 nm, domestic | Required | Category I |
| Inspected vessel — passengers for hire | International voyage | Required | Category I |
| Ocean service vessels (SOLAS) | Any international | Required + SART in survival craft | Category I + SART |
Source: 46 CFR 25.26 and NVIC guidance. Always verify requirements against your specific COI and applicable regulations for your route and tonnage.
NOAA Registration & Inspection Schedule
NOAA Beacon Registration
- ▸Register at beaconregistration.noaa.gov — free
- ▸Link your beacon's 15-digit hex ID to vessel name, type, and color
- ▸Provide 24/7 emergency contact (someone who knows your float plan)
- ▸Update registration if vessel is sold, renamed, or beacon replaced
- ▸Re-register every 2 years (NOAA sends reminders)
- ▸Failure to register: civil penalties up to $10,000
Annual Inspection Checklist
How to Self-Test an EPIRB
Check the time
Self-tests must only be performed during the first 5 minutes of any UTC hour. Outside this window, the satellite system may treat the signal as a real distress.
Activate the self-test
Press and hold the TEST button per the manufacturer's instructions (typically 3–5 seconds). Do NOT press the full ACTIVATE/DISTRESS button.
Observe indicators
The beacon indicator LED should flash or illuminate. An audible beep confirms signal transmission. Duration varies by model — typically 1 or 3 sweeps.
Confirm result
A successful self-test confirms the transmitter circuit and battery are functional. It does not confirm satellite reception — only that the beacon is transmitting.
False Activation: What to Do
- 1.Turn off the EPIRB immediately
- 2.Contact the nearest USCG Sector or District by phone
- 3.Also call on VHF Channel 16 to notify local traffic
- 4.Provide vessel name, registration/MMSI, and beacon hex ID
- 5.Document the incident — time, location, cause
- 6.Failure to report = separate civil violation
Penalty Scale
The USCG tracks false activations by vessel. Repeat violators face escalating civil penalties. A single unreported false activation can result in fines up to $10,000. Intentional false distress signals carry criminal penalties.
SART & AIS-SART: Radar-Based Rescue Devices
Traditional SART (9 GHz Radar)
A Search and Rescue Transponder responds to X-band (9 GHz) radar pulses from ships or aircraft. When interrogated, the SART transmits a series of 12 equally-spaced dots on the rescuer's radar display, extending in a straight line away from the vessel. As the rescuer closes in, the dots arc into concentric circles and eventually display as a solid blip.
- ▸Detection range: ~8 nm from ship, ~30–40 nm from aircraft
- ▸Operates on 9 GHz (X-band) only — not S-band radar
- ▸Should be held at least 1 meter above sea level
- ▸12 dots on radar display = SART in range
- ▸SOLAS: required in survival craft on applicable vessels
- ▸Battery: 96 hours standby, 8 hours active transmit
AIS-SART (Modern Alternative)
AIS-SARTs transmit a distress signal on AIS frequencies (VHF Ch 87B/88B) as a Class B AIS target. Any AIS-equipped vessel within VHF range sees the distress message on their chartplotter with GPS-accurate position.
- ▸Appears as a distinctive AIS target on chartplotters
- ▸GPS-accurate position — no bearing/ranging needed
- ▸Range: VHF radio range (~20–30 nm)
- ▸Does NOT require radar — works with AIS receiver
- ▸Does NOT appear on radar display (unlike traditional SART)
AIS-EPIRB
Combines 406 MHz satellite distress with simultaneous AIS broadcast on Ch 87B and 88B. Nearby vessels receive an immediate distress alert with GPS position while the satellite system alerts the Coast Guard. The AIS component updates position every minute during active distress.
Exam Tips
Cat I vs Cat II = auto vs manual
Category I = hydrostatic release = floats free automatically. Category II = manual only. This distinction appears on almost every exam set.
The HRU is part of the bracket, not the beacon
Expired HRU = Cat I behaves like Cat II. The HRU expires every 2 years. The battery expires on the date printed on the label (typically 5 years).
406 MHz = satellite; 121.5 MHz = homing
406 MHz is the distress frequency for Cospas-Sarsat. 121.5 MHz is the homing frequency SAR aircraft use to home in once on-scene. Know both.
SART = 12 dots on X-band radar
When a SART is detected, it shows as 12 equally spaced dots extending on the radar display. As you close range, dots become arcs, then concentric circles.
PLB ≠ EPIRB for carriage requirements
A PLB is personal, not vessel-mounted. It cannot legally substitute for an EPIRB where one is required by USCG regulations. The exam will test this.
Self-test window = first 5 minutes of any UTC hour
Only test your EPIRB in the first 5 minutes of any UTC hour. The Cospas-Sarsat system is programmed to recognize this window as test mode.
NOAA registration is mandatory
Registration links your 15-digit hex ID to your vessel. Civil penalty for non-registration. The exam may ask what information NOAA uses to contact rescuers.
False activation = must report to USCG immediately
Turn off the EPIRB, then call Coast Guard on Ch 16 and by phone. Failure to report is a separate violation from the false activation itself.
Frequently Asked Questions
What is the difference between a Category I and Category II EPIRB?
A Category I EPIRB activates automatically when it floats free of a sinking vessel (via hydrostatic release) and can also be manually activated. A Category II EPIRB is manually activated only — it does not have an automatic float-free capability. USCG regulations require Category I EPIRBs on certain vessel classes because automatic activation is critical when crew may be incapacitated.
Why must EPIRBs be registered with NOAA?
Registration with NOAA's Beacon Registration Database links your 406 MHz beacon's unique 15-digit hex ID to your vessel, contact information, and emergency contacts. When your beacon activates, Cospas-Sarsat satellites decode the ID and relay it to NOAA, which contacts the registered owner to confirm the distress and dispatch the Coast Guard. Unregistered beacons still trigger a response, but rescuers have no information about the vessel, owner, or who to contact — significantly slowing response. Failing to register or update registration is a federal violation subject to civil penalties.
How often does an EPIRB battery need to be replaced?
EPIRB batteries must be replaced by the expiration date printed on the battery label, which is typically every 5 years. The hydrostatic release unit (HRU) that triggers automatic deployment on a Category I EPIRB also has a separate 2-year expiration and must be replaced independently. Both expiration dates must be current for the EPIRB to be considered in compliance.
What happens if my EPIRB activates accidentally?
Immediately turn off the EPIRB and contact the nearest Coast Guard Sector or District by phone or VHF Channel 16 to report the false activation. Provide your vessel name, MMSI, and EPIRB registration number. Failure to report a false activation can result in civil penalties. The Coast Guard tracks repeat false activations, and vessels responsible for multiple incidents can face significant fines. Never activate an EPIRB for any purpose other than a genuine distress situation.
How do you test an EPIRB without triggering a false alert?
Most 406 MHz EPIRBs have a built-in self-test function activated by pressing and holding a test button. During the self-test, the EPIRB transmits a brief, coded test signal on 406 MHz that Cospas-Sarsat satellites recognize as a test — not a real distress. The beacon's indicator light and/or audible alarm confirm the unit is operational. Self-tests should only be performed during the first 5 minutes of any UTC hour, as Cospas-Sarsat is programmed to recognize that window as test mode. Never perform a test outside of this window.
What is a SART and how does it differ from an EPIRB?
A Search and Rescue Transponder (SART) is a radar-based device that responds to X-band (9 GHz) radar pulses from ships and aircraft by transmitting a series of 12 dots on the rescuer's radar display, extending in a line toward the SART's position. Unlike an EPIRB, which sends a distress signal to satellites, a SART is only useful when a searching vessel or aircraft with radar is within approximately 8 nautical miles. SARTs are designed for use in survival craft after abandoning ship, not as a primary distress beacon.
Which vessels are required to carry an EPIRB under USCG regulations?
Under 46 CFR 25.26, uninspected vessels (recreational) used beyond 3 nautical miles are not federally required to carry an EPIRB, though it is strongly recommended. Inspected vessels (commercial) operating beyond 3 nautical miles must carry a 406 MHz EPIRB. Vessels carrying passengers for hire on international voyages or on domestic routes beyond 3 miles from shore generally require a Category I EPIRB. Specific requirements vary by vessel tonnage, route, and COI conditions — always consult your vessel's Certificate of Inspection.
What is the AIS-EPIRB and how does it improve distress signaling?
An AIS-EPIRB combines a traditional 406 MHz satellite distress signal with an AIS (Automatic Identification System) transmission. When activated, the device broadcasts a distress message on AIS channels 1 and 2 (161.975 MHz and 162.025 MHz), which any vessel within AIS range can receive and display on their chartplotter. This allows nearby vessels to respond immediately while the satellite distress signal is relayed through Cospas-Sarsat. The AIS component provides GPS-accurate positioning and vessel identification, significantly reducing search area for rescuers.
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