A needle guard device mountable to a pre-filled syringe in its ready-to-fill state. The device includes a lock collar and a device shield biased to move relative to the lock collar. The lock collar interfaces with the syringe neck to attach the device to the syringe. A flexible member interconnects the lock collar and device shield. With the removal of a needle shield assembly comprising rigid and soft needle shields, the device shield is free to move proximally along the syringe neck. As the device moves proximally, rotation arms of the lock collar interact with angled cutouts in the device shield, causing the device shield to rotate relative to the lock collar disengaging one or more keys on the device shield from one or more keyways in the lock collar triggering the device shield to move from a first configuration in which the device shield is retractable to expose a syringe sharp to a second configuration in which the device shield is fixedly positioned to cover the syringe sharp.