A SoCal company is developing technology that can deliver highly focused beams of sound at shoppers, browsers and passers-by, enticing them to look at displays, sample products and maybe even eat McDonald's. As the WSJ tells us:
... Donna Now was caught off-guard by a subtle voice above the corned beef. Glancing up, she saw a plasma screen bursting with color and seeming to address only her. The voice pitched a special on Sara Lee honey turkeys and brown-sugar hams.
"It's pretty powerful," Ms. Now said. "I mean, I'm a vegetarian, but this makes you want to buy that ham."
... In tests at retail stores, these laserlike sound beams pinpoint individual shoppers to encourage buying with recorded messages. At some Wal-Marts that have in-store McDonald's, for example, shoppers heard messages extolling the fast-food outlet's offerings.
Here's a more technical explanation from Appliance Manufacturer magazine.