The latest ad for the fried-chicken chain is imbedded with a special, high-frequency sound that not everyone can hear.

The inventors of the buzzing sound claim it is too high-pitched for more mature ears since many adults start to lose their ability to hear higher frequencies around age 20.

The buzzing sound, dubbed the "mosquitotone," can be so annoying that stores in the U.K. have used it to ward off loitering teens. Of course, teens figured out their own uses for it as a cellphone ringtone that teachers can't hear in class.

For its part, KFC hopes the buzzing sound will become the "21st century dinner bell" - and get families to buy its new "Boneless Variety Bucket."

Only people who can tell where the sound starts during the ad can log onto KFC's Web site for a shot at a $10 coupon.

"The premise behind it is to get people to hear it and obviously take action," said KFC spokeswoman Laurie Schalow. "We are trying to break through the clutter and get people to pay attention to our TV spots."

With the all the protests over junk-food ads and childhood obesity, KFC swears it isn't aiming the ads at kids.

"It's really not meant to target 20-year-olds and under," Schalow said. "We actually found there were quite a few people in their 30s who can hear it just fine."

The ad is airing on the major broadcast channels with the exception of Fox, which was concerned that people would be startled by the sound seemingly coming out of nowhere. There's no disclaimer on the ad since that would, well, ruin the surprise.