A lockable holster includes a shroud having an elongated opening to receive a handgun with the grip of the handgun outside the shroud. A biasing member at the first end of the shroud applies a biasing force on the firing end of the handgun to bias opposite end of the handgun into engagement with the locking arrangement at the opposite second end of the shroud to secure the handgun in the shroud. In another non-limiting embodiment of the invention, the holster is mounted on a plate having fasteners passing through elongated slits into the top of the shroud to angle the shroud relative to the plate, and the plate is mounted for vertical adjustment on a U-shaped securing clamp. The holster further includes mechanical arrangements which prevent unauthorized removal of the handgun from the shroud, prevents firing the handgun when in the shroud, and signals a loaded handgun in the shroud.