In signals intelligence (SIGINT), non-communications signals are any signals sent out for a purpose other than communicating information.
This includes radar emissions and emissions from instrumentation (which provide information, but are not sent out for the purpose of providing information to others).
[1][2][3] Electronic signals intelligence (ELINT), which came to be studied in great detail after World War II, attempts to detect and analyze enemy non-communications signals.
[3][4] Foreign instrumentation signals intelligence (FISINT) focuses specifically on non-communications signals emitted by instrumentation, including telemetry signals sent between components of a system.
This article relating to communication is a stub.