Abstract: A gunshot detection system provides an audio and visual surveillance system, embodied within a Gunshot Detector (GSD) attached to a building's walls and ceilings and a Firearm Event Detector (FED) worn on a person's outer clothing. In both embodiments, the system of the invention detects the physical signatures of a firearm discharge, specifically sound from a muzzle blast and light from a muzzle flash. The system would be linked to a software program and/or electronic transducer(s) and/or microprocessor(s) and/or electronic Logic Circuitry (using algorithms, logic gates) that would apply one or more identification algorithms to distinguish firearm discharge from other signals. Either embodiment may be linked to an emergency notification system or to a “Guardian Barrier System” (GBS) wherein a facility or premises, for example a school, is equipped with electromagnetically releasable and electromagnetically lockable doors such that facility or premises may be automatically locked down.