Are your teenagers tuning into a cell phone ring tone that you can't hear? In places where cell phones are forbidden, crafty kids are avoiding detection by using a ring tone that is inaudible to grownups. Although most human communication takes place in a frequency range between 200 and 8,000 Hz, most adults' ability to hear frequencies higher than that begins to deteriorate in early middle age. Ironically, the popular ring tone is a modified version of an "ultrasonic teenage repellant" that was designed to keep loitering teens away from storefronts. Click here for more information. You can also try to listen to the ring tone.