Signals Intelligence

States gather information about other states, about armies, and about individual people. One of the most important sources for this are signals: anything someone sends via radio, telephone, satellite, or the internet. Signals Intelligence is the technical term for intercepting and analyzing such transmissions. Responsible for this are state intelligence agencies, in Germany primarily the Bundesnachrichtendienst, and in the USA the National Security Agency. The term encompasses two things: the content of a message and its technical accompanying data. Even the second part often reveals a great deal, even when the content itself is encrypted and thus unreadable.

Why radio messages decide wars

Whoever knows what the enemy is planning has to guess less. The most famous example comes from the Second World War. British specialists at Bletchley Park cracked the German cipher machine Enigma, which was used to encrypt radio messages. Historians estimate that this shortened the war by months to years. This work also incidentally produced the first programmable computing machines.

Today, SIGINT is politically sensitive because the technology also affects civilian networks. The same cables and mobile phone masts carry government communications and private chats alike. In 2013, former intelligence employee Edward Snowden published documents about the scope of such programs. The result was a years-long debate about surveillance, fundamental rights, and parliamentary oversight of intelligence agencies.

The topic also plays a role economically. Companies fear that competitors or foreign states might capture their development data. This is an important reason why encryption in products is now standard. Those purchasing cloud services now regularly ask in which country the data is stored.

From antenna mast to automated analysis

It always starts with recording. For this there are antenna installations, surveillance ships, reconnaissance aircraft, satellites, and tapping points on fiber-optic cables. The volume is enormous: a single undersea cable transmits more data than a person could read in many lifetimes. That’s why filtering happens before anyone even looks at it.

Then comes the analysis. Two levels are distinguished here. Content analysis reads along with what was said, and often requires decryption first. Traffic analysis only looks at the accompanying data: who spoke with whom, when, and for how long? This metadata is usually unencrypted and still reveals social networks and movement patterns.

This is where AI comes into play. Speech recognition automatically converts recordings into text, machine translation makes foreign languages accessible. Pattern recognition searches for anomalies, such as a sudden sharp increase in radio traffic at a border. This is also the biggest weakness: algorithms deliver suspicions, not proof, and false alarms affect innocent people. A common misconception is also that encryption renders SIGINT useless. It protects the content, not the fact that a device transmitted from a certain location.

SIGINT in the news and in your own pocket

In the news, the term mainly appears in connection with wars and crises. During the Ukraine war, media repeatedly reported on intercepted Russian radio traffic. Reports on NATO reconnaissance flights over the Baltic and Black Seas also belong to this field. For classification, the distinction helps: HUMINT means information from human sources, i.e. spies, IMINT means satellite and aerial imagery. SIGINT is the electronic branch of this.

In everyday life, one encounters the topic indirectly through technology designed to protect against eavesdropping. Messengers like Signal or WhatsApp advertise end-to-end encryption. The small padlock in the browser means the connection is encrypted. Both are a direct response to the possibility of lines being intercepted.

For investors and companies, SIGINT is also a market. Firms sell eavesdropping technology, analysis software, and spyware for smartphones to government agencies. The case of the Pegasus software showed that such tools were also used against journalists. Legislators in Europe have since been working on stricter export and deployment regulations.