A digital distress alert can cross distance in seconds, carrying identity and sometimes position. It solves the first problem—getting attention—but not every question a rescue coordinator must answer.
What automation does well
Digital systems are designed to raise an alarm rapidly and consistently. Depending on the equipment and service, an alert may identify a station, provide a position and indicate a broad distress category. A DSC distress alert, for example, carries the MMSI, a position with the time it was valid, and the nature of distress if selected from a fixed list such as fire, flooding, collision, grounding, sinking or abandoning ship.1,2 406 MHz beacons are detected by the Cospas-Sarsat satellite system far beyond normal VHF range;3 DSC sends an automatically formatted alert to equipped stations without relying on someone first recognising a spoken call.4
This reduces dependence on perfect voice conditions at the most stressful moment. It also gives responders structured data that can be compared with registrations and other reports.
The alert is the beginning
A rescue coordination centre still needs a changing operational picture. How many people are at risk? Is there fire, flooding or a medical emergency? Is the vessel abandoned, drifting or manoeuvrable? What survival equipment is available? Are there hazards to rescue units?
No compact alert format can fully describe this evolving situation. Voice communication, messages through other vessels and updates from rescue units allow coordinators to test assumptions and adjust the response.
Registration connects a signal to reality
Beacon and MMSI records can provide vessel and emergency-contact information. In the United States, for example, owners of U.S.-coded 406 MHz beacons are required by law to register them with NOAA, so that the system can quickly identify the beacon’s owner in an emergency.5 If those records are missing or outdated, authorities may have to spend valuable time establishing whether an alert is genuine and what they are looking for. Registration does not replace an alert; it makes the alert more intelligible.
False alerts also need people
Automatic systems can be activated accidentally or because equipment is mishandled. NOAA reports that 98 % of all 406 MHz beacon activations are false alarms—and that registration means most inadvertent activations are resolved with a phone call.6 Even so, responders cannot simply assume that an unusual alert is false. They use registrations, attempted contact, corroborating information and operational judgement to assess it. Prompt cancellation through the appropriate channel can prevent resources from being committed unnecessarily. For an inadvertent VHF DSC alert, the U.S. Coast Guard’s instructions are to switch off, switch on again on channel 16 and broadcast “All stations, all stations, all stations, this is [name, call sign, MMSI, position]. Cancel my distress alert of [date, time UTC].” An EPIRB alert is cancelled by contacting a coast station or RCC. No action is normally taken against anyone who reports and cancels a false alert.7 Exact procedures can vary by system and authority.
Communication after the first contact
As an incident develops, information may pass between a casualty, coast station, rescue coordination centre, aircraft, lifeboats and nearby vessels. Each participant sees only part of the event. Human communication turns those separate observations into shared situational awareness.
Automation is therefore best understood as a strong first link in a longer chain. It can make discovery faster and more reliable. People still interpret, verify, prioritise and coordinate.
Sources and further reading
- ITU-R Recommendation M.541-11 (2023). Operational procedures for the use of digital selective-calling equipment in the maritime mobile service.
- ITU-R Recommendation M.493-16 (2023). Digital selective-calling system for use in the maritime mobile service, Table A1-3.
- Cospas-Sarsat. Cospas-Sarsat system.
- U.S. Coast Guard Navigation Center. Digital Selective Calling.
- U.S. Coast Guard Navigation Center. SARSAT beacons.
- NOAA SARSAT. Preventing false alerts.
- U.S. Coast Guard Navigation Center. Instructions for cancelling a false distress alert.
- International Maritime Organization. Radiocommunications.
Editorial note: This article describes principles common to modern maritime alerting and SAR. Equipment capabilities, shore arrangements and follow-up procedures vary. It is not a substitute for approved GMDSS training. Last fact-checked: 3 October 2026.
