An anti-theft device having at least three side surrounding frames in series, each having an adjustable width. The first side surrounding frame has a first free end and a second end rotatably secured to a first end of a second side surrounding frame. The second end of the second side surrounding frame is rotatably secured to a first end of a third side surrounding. The second end of the third side surrounding frame or the second end of the last side surrounding frame is a free end. When the anti-theft device is in a folded state, the at least three side surrounding frames stack on each other with the rotatably secured ends of the various side surrounding frames remaining rotatably secured to each other. The device is arranged around an AC unit and two free ends lock together to enclose the AC unit within the plurality of side surrounding frames.