In a door lock, a locking mechanism includes an outer wheel, an inner wheel disposed inside the outer wheel and operable to rotate relative to the outer wheel, a clutch member disposed in the inner wheel and normally biased to radially extend from the inner wheel into the outer wheel to interengage the inner and outer wheels, and an arm plate sleeved around the inner wheel. When the inner wheel rotates in a first direction, the arm plate is driven by the inner wheel to actuate the deadbolt. When the inner and outer wheels are interengaged, the inner wheel drives the outer wheel by rotating in a second direction. When the inner wheel disengages from the outer wheel, rotation of the inner wheel in the first or second direction is idle relative to the outer wheel.