An international distress frequency is a radio frequency that is designated for emergency communication by international agreement.
For much of the 20th century, 500 kHz was the primary international distress frequency. Its use has been phased out in favor of the Global Maritime Distress Safety System.
Use of some distress frequencies is permitted for calling other stations to establish contact, whereupon the stations move to another frequency. Such channels are known as distress, safety and calling frequencies.
Satellite processing from all 121.5 or 243 MHz locators has been discontinued. Since February 1, 2009, the U.S. Coast Guard only monitors distress signals from emergency position indicating radio beacons that broadcast using digital 406 MHz signals. Digital 406 MHz models became the only ones approved for use in both commercial and recreational watercraft worldwide on January 1, 2007.
International distress frequencies, currently in use are :
2182 kHz for medium range maritime voice use. The US Coast Guard has said "beginning August 1st, 2013 the Coast Guard would no longer monitor 2182 kHz", as have many other coast guard services.
Several HF maritime voice frequencies exist for long-distance distress calls:4.125 MHz
6.215 MHz
8.291 MHz
12.290 MHz
16.420 MHz
121.5 MHz is the civilian aircraft emergency frequency or International Air Distress frequency. It is used by civilian distress radiobeacons; however, the Cospas-Sarsat system no longer monitors the frequency.
243 MHz for NATO military aircraft emergency frequencies
Marine VHF radio Channel 16 (156.8 MHz) for short range maritime use
406 MHz to 406.1 MHz is used by the Cospas-Sarsat international satellite-based search and rescue (SAR) distress alert detection and information distribution system
462.675 MHz is a UHF mobile distress and road information calling frequency allocated to the General Mobile Radio Service and used throughout Alaska and Canada for emergency communications; formerly called Orange Dot in the 1960s, "GMRS 675" or Channel 6 on mobile radios today. Its bandwidth can vary between 12.5, 25 and 50 kHz, and is also allocated to Ch. 20 on 22-channel FRS/GMRS "blister pack" radios. It can have a repeater input frequency of 467.675 MHz, and a tone squelch of 141.3 Hz.
Several maritime frequencies are used for Digital Selective Calling (DSC), and they are also monitored for DSC distress signals:
2.1875 MHz
4.2075 MHz
6.312 MHz
8.4145 MHz
12.577 MHz
16.8045 MHz
156.525 MHz, Marine VHF radio Channel 70
Emergency Centre of Activity (ECOA) frequencies informally established by the International Amateur Radio Union regional organizations (frequencies shown in kHz):
Emergency/Disaster Relief Interoperation Voice Channels of the amateur radio Global ALE High Frequency Network:3791.0 kHz USB
7185.5 kHz USB
10145.5 kHz USB
14346.0 kHz USB
18117.5 kHz USB
21432.5 kHz USB
24932.0 kHz USB
28312.5 kHz USB
Citizens band (CB) radio (not available in all countries)
Emergency channels 9 (27.065 MHz AM) and 19 (27.185 MHz AM)
