Russia’s chilling doomsday radio station UVB-76 has sent out four signals in just 24 hours. Also known as “The Buzzer”, it has been used by the KGB since the Cold War and has been sending cryptic messages ever since. On Tuesday, the station signalled four words, according to Telegram channel UVB-76 logs. These were: Neptune, Thymus, Foxcloak, and Nootabu.

The channel, which constantly logs the station’s activity, said the radio buzzed the eerie messages within 24 hours, which is highly unusual. Speculation over the meaning behind the signals include codes for secret military operations, yet its purpose remains a mystery. The Buzzer transmits messages on the frequency 4625 kHz which is a chilling sound, ringing nonstop. However, when a significant event happens such as a nuclear attack, messages are sent out through the channel.

In February, UVB-76 released a staggering 25 messages within 24 hours, according to Russian state media, which include: Synopsis, Boulevard, Coarsening, B*******, Optoshum, Elecbase, Shtatognome Commissar and Volkokran.

The mystery station has sparked numerous theories, with the most common being a military communication tool. Some have rumoured it to be a “dead man’s switch” system, automatically triggering a military response if Russia became under attack.

The Buzzer has been ringing since the late 70s which was brought to the attention of a senior researcher in electronic warfare in the 1990s.

Professor David Stupples told the Sun that the buzzing sound is available for anyone in Russia to listen to. He added that the signal can be sent and heard without satellites or the internet.

"What that means is that the signal never leaves the atmosphere,” he told the newspaper.

"It just bounces along what is called the ionosphere. It would cover basically the whole of Russia."

He added that, in an event where communication would be wiped out, President Putin’s UVB-76 would still work “as normal”.

The researcher added that the reason the broadcast of the buzz is continuous is for Russia to reserve the frequency. This means no one is able to “snatch” the signal - a risk if the sounds stopped.