What Happens When You Press an EPIRB?
What Happens When You Activate an EPIRB? — The Full Picture
Most people who carry an EPIRB have never actually activated one in a real emergency — and that is a good thing. But most people also do not know exactly what happens when they do. Understanding the process matters because it changes how you think about the device, and why registration is so much more than a box-ticking exercise.
Here is the exact sequence from the moment you press the button.
Step 1 — The Signal Goes Up
The moment your EPIRB is activated — either manually by pressing the button, or automatically when a Category 1 device hits water — it begins transmitting on 406MHz. This signal is picked up by the Cospas-Sarsat satellite network, a global system of search and rescue satellites operated by an international consortium including the US, Russia, Canada, and France.
If your EPIRB has GPS — and any modern one should — your exact position is included in that first transmission. Satellites in geostationary orbit can receive and relay this signal almost instantly. The whole world is covered.
Step 2 — The Coastguard Receives the Alert
The satellite network relays your signal to the nearest ground station, which passes it immediately to a Maritime Rescue Coordination Centre — in UK waters, that is HM Coastguard at Falmouth or Aberdeen. They receive your unique beacon ID, your GPS position, and the time of activation.
From verified real-world activations, the coastguard is typically contacting emergency contacts within 1 to 2 minutes of activation. One documented case showed the Spanish coastguard calling an emergency contact 1 minute after a PLB was activated, with HM Coastguard calling 2 minutes later. The system is fast.
Step 3 — They Try to Contact You First
This is the part most people do not know. Before launching a full rescue response, the coastguard will attempt to contact your registered emergency contacts to confirm whether the activation is genuine or accidental.
This is exactly why registration matters so much. An unregistered EPIRB signal requires the coastguard to investigate from scratch — who owns it, what vessel it is on, where that vessel should be. That takes time. A registered EPIRB (at the UK Beacon Registry) with up-to-date contact details means the coastguard can verify a genuine emergency in minutes and get resources moving immediately.
An out-of-date registration caused a 6-hour search involving a coastguard helicopter, two RNLI lifeboats, and police for a vessel that was safely moored in a marina with an EPIRB that had been left on board after the boat was sold. The new owner had never updated the registration. Six hours of rescue service time wasted.
Step 4 — Rescue Assets Are Dispatched
Once the activation is confirmed as genuine, the Maritime Rescue Coordination Centre coordinates the response. Depending on your location, this may include an RNLI lifeboat, HM Coastguard helicopter, a nearby commercial vessel, or all three. Your GPS position means they know exactly where to go.
The EPIRB simultaneously transmits on 121.5MHz — a homing signal that allows rescue aircraft and vessels to home in on your exact position as they get closer.
Step 5 — Keep It Transmitting
Do not switch the EPIRB off unless the coastguard specifically tells you to. Even after you have made VHF contact with a rescue vessel, the EPIRB signal helps guide them to you and provides a continuous position update. Keep it on and keep it pointing skyward.
If you are in a liferaft, float the EPIRB alongside tethered to the raft so the antenna remains vertical and above the waterline. A submerged antenna transmits poorly.
What If It Was an Accident?
Accidental EPIRB activations happen. If yours fires accidentally, contact HM Coastguard immediately on VHF Channel 16 or by telephone. Give them your beacon’s HEX ID number — the unique 15-character code printed on the device — and confirm it was accidental. This cancels the response quickly. Without the HEX ID, cancellation takes much longer.
Keep the HEX ID somewhere accessible. Write it in the ship’s log. Keep a copy ashore with your emergency contacts.
The Visual — How It All Connects
Think of it as three layers working simultaneously:
Satellite layer — 406MHz signal goes up, Cospas-Sarsat picks it up globally, your GPS position is relayed to a ground station within minutes.
Coordination layer — HM Coastguard receives the alert, contacts your emergency contacts, confirms the emergency, dispatches assets.
Homing layer — 121.5MHz signal guides rescue vessels and aircraft to your exact position as they arrive in your area.
Each layer backs up the others. If GPS fails, Doppler positioning can still locate you. If satellite coverage is momentarily reduced, the 121.5MHz homing signal guides rescuers in. The system is designed to be redundant.
FAQs
How quickly will someone reach me after I activate an EPIRB?
It depends entirely on your location and the resources available. In UK coastal waters, RNLI lifeboats can be on scene within 30 to 90 minutes in many areas. HM Coastguard helicopters cover most of the UK coastline within similar timeframes. Offshore, response times will be longer — which is exactly why EPIRBs transmit for a minimum of 48 hours.
What is the HEX ID on my EPIRB?
A unique 15-character identification code assigned to your beacon. It is printed on the device and used to identify who you are when the signal is received. You need it to register your EPIRB and to cancel a false alarm quickly.
Does an EPIRB work anywhere in the world?
Yes. The Cospas-Sarsat network provides global coverage. An EPIRB activated in the middle of the Pacific Ocean will reach a rescue coordination centre. Response times in remote areas will be longer but the signal will be received.
The information in this article is for general guidance only. Always verify current beacon registration requirements at beaconregistration.admiralty.co.uk and gov.uk/mca. marinesafetyguide.com participates in affiliate programmes including Amazon Associates and the Awin network and may earn a small commission on purchases made through links on this site, at no extra cost to you.
