Ear blasting

TOKYO (Reuters) - A Japanese park has started playing a high-pitched tone at night that only young people can hear to help drive away teenagers who keep vandalizing... "The Mosquito" is a device that emits a high-frequency tone that is unbearable to those who can hear it... People's ability to hear high frequencies falls as they age.
The device produces a high-pitch tone of around 17 kilohertz, which teens can hear but older people cannot.