The distress signal: how emergency calls save lives at sea, in the air and at work
From the Baltimore bridge collapse to lone workers in Germany, the distress signal remains a vital tool for summoning help — and its use is governed by clear rules and new technology.
A distress signal (Notsignal) is a nonverbal emergency call used to request help acoustically or visually. Which signal is used depends on the situation, the available means and the surroundings. The best-known distress signal is SOS, recognised worldwide at sea, in the air and on land.
In March 2024, the crew of a container ship off Baltimore sent a distress signal moments before the vessel struck and brought down the Francis Scott Key Bridge. Much of the evidence afterwards pointed to an accident, but the call itself gave a warning before the collapse. Seventeen years earlier, in January 2007, the distress signal of a missing Adam Air Boeing 737-400 carrying 102 people went silent over Indonesia. A distress signal — Notsignal in German — is a nonverbal emergency call, sent acoustically or visually, to request help. Which signal is used depends on the situation, the means available and the surroundings. The best known is SOS, but the principle extends far beyond Morse code, from ships and aircraft to workers alone on a factory floor. The question of how such calls are made, and who is required to be able to make them, has fresh relevance. Germany obliges employers to equip lone workers with personal emergency signal systems, and manufacturers are now competing to supply them.
What a distress signal is and how it is used
A distress signal is a nonverbal emergency call, used to request help when spoken or written communication is impossible or impractical. It can be made acoustically — by sound — or visually, by light, flags, fire or movement. Which signal is appropriate depends on the situation, the means available to the person in danger, and the surroundings: what works on open water may be useless in a forest or a factory. The best-known example is SOS, the internationally recognised Morse code sequence of three short signals, three long ones and three short ones again. Whatever form it takes, the purpose is always the same: to alert others that help is needed, fast.
Distress calls in major disasters, from Baltimore to Indonesia
When the container ship struck the Francis Scott Key Bridge in Baltimore in March 2024, the crew had already sent a distress signal before the collapse. In the aftermath, much of the evidence pointed to an accident rather than any deliberate act.
Seventeen years earlier, a distress signal marked the last trace of another disaster. In January 2007, an Adam Air Boeing 737-400 carrying 102 people went missing in Indonesia. Its distress signal went silent, and with it the clearest indication of the aircraft's fate.
Distress calls have also prompted successful interventions. According to reports, a Lufthansa aircraft travelling from Johannesburg to Frankfurt transmitted an international distress signal and was diverted for an emergency landing. The timing of the incident, the landing location and the cause of the emergency have not been confirmed.
Together, these cases show the dual role of the distress signal in major emergencies: it can summon help in time to avert the worst, or it can become the final message from a crew that could not be saved.
The distress signal of a missing Adam Air Boeing 737-400 carrying 102 people in Indonesia went silent.
The crew of a container ship sent a distress signal before the Francis Scott Key Bridge in Baltimore collapsed.
After the Baltimore bridge collapse, much of the evidence pointed to an accident.
Germany's rules on emergency signals for lone workers
German law places specific duties on employers whose staff work in isolation. According to haufe.de, employers must provide a personal emergency signal system whenever an employee works alone and beyond the call and sight range of other workers. The requirement is designed to ensure that someone in distress can summon help even when no colleague is nearby to notice.
Technology providers have moved to meet that obligation. According to industry sources, Spectralink and tetronik both offer personal emergency signal systems intended to protect lone workers. Such systems allow an isolated employee to trigger an alert and reach assistance quickly, closing the gap that solitary work creates. For employers, the message from the rules is straightforward: where a worker is out of earshot and out of view, a reliable means of raising the alarm is not optional but mandatory.
Multitone's EkoTek system debuts at the A+A trade fair
Multitone used the A+A trade fair in Düsseldorf to present its EkoTek personal emergency signal system publicly for the first time, according to openpr.de. The system is designed to protect lone workers, a group for whom German employers must provide a personal emergency signal solution when staff work alone and out of call and sight range of colleagues. Multitone is not alone in this market; Spectralink and tetronik also offer personal emergency signal systems aimed at the same need, according to the same reports.
What distinguishes EkoTek, according to the company's presentation, is how it achieves coverage. The system builds its radio network using repeaters, which extend the signal across a wide area so that workers remain reachable throughout a site rather than only near a single transmitter. The radio repeaters are described as long-lasting, a claim intended to reassure operators about maintenance demands once the network is installed.
Frequently asked questions
What is a distress signal (Notsignal)?
A distress signal, known in German as a Notsignal, is a nonverbal form of emergency call used to request help acoustically or visually in an emergency situation. Which signal is used depends on the situation, the available means, and the surroundings. The best-known distress signal worldwide is the SOS signal.
What happened with the distress signal before the Baltimore bridge collapse?
In March 2024, the crew of a container ship sent a distress signal before the Francis Scott Key Bridge in Baltimore collapsed. After the collapse, much of the evidence pointed to an accident. It is not yet known whether the crew's distress signal led to any rescue or evacuation measures, or what the final outcome of the accident investigation was.
What happened to the Adam Air flight in Indonesia in 2007?
In January 2007, the distress signal of a missing Adam Air Boeing 737-400 carrying 102 people on board in Indonesia went silent. The briefing available does not say what happened to the aircraft after its signal went silent, so that part of the story remains unconfirmed here.
Did a Lufthansa flight send a distress signal?
According to reports, a Lufthansa aircraft traveling from Johannesburg to Frankfurt transmitted an international distress signal and was diverted for an emergency landing. The timing of the incident, the location of the emergency landing, and the cause of the emergency are not confirmed in the available material.
What is a personal emergency signal system for lone workers in Germany?
According to haufe.de, German employers must provide a personal emergency signal system when an employee works alone and out of call and sight range of other workers. Reports say Spectralink and tetronik offer such systems to protect lone workers. Multitone presented its EkoTek system, which builds a radio network using long-lasting repeaters for area-wide coverage, at the A+A trade fair in Düsseldorf.
Compiled from reporting by 6 independent outlets. How we source our reporting.
