It will rely on an infrared LED to project a light onto the glass, where an IR camera that is sensitive enough picks up the scattered light particles which your finger touches create, registering each touch (accidental or not) into a registered press. Without any tactile feedback, it is the same as typing on those laser-based keyboards of previous generations, but at least the keys on this will be backlit to enable you to work under dark conditions. Perhaps enough interest in the Multi-touch Keyboard might see a pressure-sensitive key version in the pipeline. Expect to place your first orders within the next three months.