The international emergency signal for distress is the repetition of three of any signal, such as three short blasts on a whistle, three flashes of light, three gunshots, or three fires arranged conspicuously. This "three of any" signal is widely recognized to indicate distress and request immediate assistance. Additionally, the spoken distress call "Mayday, Mayday, Mayday" is used in voice-radio communications to signal grave and imminent danger requiring urgent help. The Morse code SOS (three short, three long, three short signals) is also internationally recognized as a distress signal, especially in non-voice communications. Other recognized distress signals include visual signals like red flares, orange smoke, signaling flags (NC), and continuous sound signals like foghorn blasts. Emergency Position Indicating Radio Beacons (EPIRBs) and digital selective calling on marine radios also send distress alerts. In summary, the core international distress signals are:
- Three repeated signals of any kind (sound, light, fire)
- "Mayday" spoken three times for voice radio
- SOS in Morse code (· · · — — — · · ·)
These signals are universally understood as calls for emergency help.
