X20 kHz Frequency (24 & Younger can hear)
x8 kHz Frequency (Everyone can hear)
X10 kHz Frequency (60 & Younger can hear)
X12 kHz Frequency (50 & Younger can hear)
The Mosquito or Mosquito alarm is a machine used to deter loitering by young people by emitting sound at high frequency, in some versions so it can be heard mostly by younger people. The devices have attracted controversy on the basis of human rights and discrimination concerns.