The computer generates dolphinlike whistles and clicks. Touch screens employ one of three physics principles for detecting the point of touch. In other designs, a finger or stylus interrupts a standing pattern of acoustic waves or infrared lights that blanket the surface. Capacitive screens must be touched by a finger or an electrically grounded stylus to conduct current. Wave screens are the newest and most expensive.
Most people are unaware of the type of screen they are using.
But tricks can help you tell, according to Frank Shen of Elo TouchSystems in Fremont, Calif., the largest U.S. maker. If it responds, it could be resistive or infrared. In this case, place two separated fingers against the screen at the same time. If the unit does not respond to your fingernail, again place two separated fingers against it.