An antitheft device adapted for attachment to the valve stem of an inflated vehicle tire may comprise: a plunger assembly including a plunger engageable with a valve core of the valve stem and axially movable relative thereto for forcing the valve core to an open position releasing air from the tire; and an actuator assembly including a cam member radially movable with respect to the axis of the plunger in response to rotation of the vehicle tire, from a passive position to an active position forcing the plunger toward opening of the valve core.
