The anti-teen machine
Pretty nifty. And annoying. Visit Compound Security, a UK firm specialising in this teen control product. It’s quite painful to experience actually.
Got it from an SMH article about a teen ring tone, which is a 17Khz ringtone that only teens can hear, letting them know calls/SMSs are coming in without adults like teachers/parents knowing. It plays fine through the computer speakers, and boy is it piercing.