A seat belt buckle (100) operable with a pretensioner (330) comprising: a frame (102) having a first latch opening (126a) therein, and opposing frame sides (108a,b), each side including a latch plate slot (110) arranged generally perpendicular to the direction of movement of a tongue into the buckle and pivoted weight mechanism (112, 200, 220). The buckle additionally includes a latch plate (180), having portions (186) movable within the latch plate slots between a locked position in engagement with an opening within the tongue and with the first latch opening (126a), the latch plate moveable between a latched position within the latch opening (126a) in the frame and within the latch opening (173) of the tongue to an unlatched position out of the latch openings. The weight (200) as it pivots generates a force upon the latch plate during operation of the pretensioner tending to keep the latch plate in the first opening and a button (250) operatively received upon the frame having ramp means (260) for lifting the latch plate to its unlatched position.