Abstract: A self-triggering inflatable balloon device. In a preferred embodiment, the device comprises a cylinder of compressed gas having an actuating valve thereon. The other end of the actuating valve is coupled to a deflated balloon. The cylinder, valve and deflated balloon are secured to the interior of a box having a lid. An actuating member of the valve is coupled to the box lid such that the valve is opened when the box lid is raised. Upon opening of the box lid, therefore, the actuating valve is opened and the balloon is automatically inflated with the gas from the compressed gas cylinder. The device may be given as a gift wrapped present or mailed to a friend, and will produce a surprise when opened.