Automatically retractable utility knife

A housing in combination with a locking mechanism which comprises:

• the housing constructed of first and second separable halves, the housing having front and rear ends and an axis extending between the front and rear ends;
• the locking mechanism comprising a resilient locking arm on the first half of the housing, the locking arm comprising i) an upstanding portion oriented generally perpendicular to the housing axis, the locking arm having a first end attached to the first half of the housing and a second end, ii) an actuating arm extending laterally from the second end of the locking arm, whereby downward force on the actuating arm results in a bending of the upstanding portion, and iii) a locking lip on the second end of the locking arm extending laterally in a direction opposite to the direction of bending of the upstanding portion during downward force on the actuating arm, the second half comprising a locking aperture sized to receive the second end of the locking arm, and a locking shoulder adjacent to the locking aperture, the locking arm and locking aperture being correspondingly positioned so as to become aligned when the halves of the housing are aligned for assembly, the locking arm extending into the locking aperture during assembly, the locking lip positively locking on the locking shoulder, wherein the locking mechanism is actuated by pressing the housing halves together in directions generally perpendicular to the axis of the housing, and wherein upon release of the locking mechanism by application of downward force on the actuating arm, the rear ends of the housing halves are separated by pulling in opposite directions generally perpendicular to the axis of the housing.