Typical military and spy messages consists of five letters and numbers groups. These are encrypted and you can come across these messages in shortwave bands. Usually these messages are read in English. To receive these messages spies need only general domestic radio with SW coverage.

Great sender of number transmissions were German Democratic Republic, in the museum you can see for example special VIP-receiver from the GDR Embassy in Helsinki. In the museum is also KGB agent transmitter-receiver R-353 and other older agent's radios.

Today best known number and letter reading stations are in Israel, Russia, Cuba but most countries are ready to activate their stations for agents in foreign countries.