Signals intelligence (SIGINT) is divided into three categories based on the type of signal collected. COMINT (Communications Intelligence) intercepts messages between people, such as radio calls and data links. ELINT (Electronic Intelligence) captures non-communication signals like radar emissions and navigation beacons. FISINT (Foreign Instrumentation Signals Intelligence) targets telemetry from weapons tests, missile launches, and satellite data links. Each type requires different receivers and different analysis techniques.