Researchers at MIT's Lincoln Laboratory, a United States Department of Defense research facility, developed laser systems that can "transmit various tones, music and recorded speech at a conversational volume" to specific people without the recipient wearing any special equipment. Basically, the operator points a laser at someone from a distance and that individual hears the transmitted audio even though others in the area don't. The new approaches are based on the photoacoustic effect, which occurs when a material forms sound waves after absorbing light. In this case, the researchers used water vapor in the air to absorb light and create...