A needle guard device (100) mountable to a pre-filled syringe (50) in its ready-to-fill state. The device includes a device shield (20) interconnected to a lock collar (10) with flexible member (30) and biased to move relative to the lock collar (10). The lock collar (10) interfaces with syringe neck (53) to attach the needle guard device (100) to the syringe (50). As the needle guard device shield (100) moves proximally, rotation arms (14) of the lock collar (10) interact with angled cutouts (23) in the device shield (20), causing the device shield (20) to rotate relative to the lock collar (10) and disengaging one or more keys (25) on the device shield (20) from one or more keyways (15) in the lock collar (10) triggering the device shield (20) to move from a first configuration in which the device shield (20) is retractable to expose a syringe sharp (51) to a second configuration in which the device shield (20) is fixedly positioned to cover the syringe sharp (51).
