As personal computers and their peripheral units become smaller and lighter, portable user interfaces, such as portable keyboards, are also required. Although a number of devices have been proposed, thus far the devices have been difficult to use because of restricted functionality or the requirement for special operational methods. This paper presents the "AirGrabber", a virtual keyboard suitable for wearable computers, by which a user can enter characters by "typing" in the air on a virtual keyboard. The AirGrabber detects keystrokes by monitoring the motions of the fingers and hand through a miniature camera and a tilt sensor on the user's wrist.