http://www.msnbc.msn.com/id/24280571
This is an interesting invention.
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This is quite old. In fact it has already become a Law and Order subject, because as the sound is only distinguishable by young kids, it has been adapted by some as cell phone ringtones so they can hear during school and not get caught while receiving calls.
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I guess it could be used to prevent toddlers and young kids ....and dogs....from going to certain areas .