Some new products work at discovering and responding to networks attacks in realtime.
Intrusion detection has a long history.
Early watchman could listen for the rustling of leaves, or a snapped twig. In World War II, soldiers would attach a string between two trees, and dangle a can containing pebbles. If the can rattled, someone was coming. More recently, infrared detectors and even doppler radar are used to detect intruders. Intrusion detection in computers also has a long history, beginning with research in the seventies.