Possible technical question: how do people detect missile launches? Do they scan the skies? Do they have sound/vibration pattern detection? Satellites?

Update: In the article I see: "Still, we have no idea what early warning system triggered the alert. America's infrared early warning space-based sensing layer stares at the earth from many vantage points in orbit day and night. Historically, it provides the initial warning of a ballistic missile launch via detection of the missile's hot boost-phase plume. These satellites, especially the newer ones, can also detect a greater variety of infrared events, as well, including artillery fire, aircraft crashes, smaller missile shots, and even the launches of cruise missiles. "