A locking bar for sliding closures having a main portion and a shorter hinged portion is described. Mounted on the main portion are two spring-loaded retractable sliding bolts, which mate with pre-drilled holes in the base of one closure frame member. The locking bar is inserted in the track of the other closure member with the sliding bolts engaging the holes, so as to prevent either closure from being opened from the outside by an intruder. However, the relatively short hinged member may be swung to an upright position by means of a recessed finger pull, thus permitting one sliding closure member to be cracked for ventilation while at the same time preventing ingress through the closure.