Abstract: A trigger-engaging plug for a firearm having of the type that is a trigger guard defining lateral openings and a trigger. A rear portion of the trigger is spaced from and in opposed relation with a portion of the firearm frame. The plug includes a base portion having a size and shape corresponding generally to one of the lateral openings. The plug also has a trigger-blocking projection extending from and positioned generally at one end of the base portion. The trigger-blocking projection defines a lock shackle-receiving bore. A tang extends from and is positioned on the base portion and in opposed relation with the first or trigger-blocking projection. The trigger-blocking and tang define a recess of a size and shape corresponding to a trigger.