A needle guard device mountable to apre-filled syringe in its ready-to-fill state. The device includes alock collar and a device shield biased to move relative to thelock collar. The lock collar interfaces with the syringe neck toattach the device to the syringe. With the removal of a needleshield assembly comprising rigid and soft needle shields, thelock collar and device shield are free to move proximallyalong the syringe neck and interact with a syringe step downarea to activate the device. As the device moves proximally,retention arms of the device shield interact with the syringestep down, causing the arms to deflect radially outwards todisengage from the lock collar triggering the device shield tomove from a first position to a second position.
