Ok, my idea is to fix two Ultrasonic sensor at each top corner of a screen and to detect when a finder cross them and calculate the position to the screen. This way, I could build a touch screen application that will be able to press button just by getting a finder to the screen. Both sensor would been parallel to the screen pointing into the opposite down corner of the screen.
It is possible? Is there something that would not make this project works? What sensor do you recommend me?