I've noticed two places on Oahu using anti-loitering devices called mosquito alarms.
They output loud chirps that are too high-pitched for most adults to hear, meaning its targeted towards children and teenagers, but I can hear them and it's incredibly irritating. (I'm in my 30s).
So far I've heard them at Walgreens Keeamoku and at the Waikiki Aston, you can hear them across the street as far as a block away.
Not sure if there's anything that can be done to stop these.
Quieter O'ahu Response:
Sorry for delayed response. Wanted to look into the ins and outs of the Mosquito System before responding.
Must admit you've caught us off-guard in the sense that this is the first contact we've had discussing this form of noise - and, from all literature - it is intended to be noise, an anti-loitering noise, targeting younger people.
For the benefit of others who may read this, human hearing, generally, is from 20Hz - 20,000Hz/20kHz. The mosquito system operates two tones: a -3dBFS steady ton at 17.4 kHz and its modulated version, oscillating between 17kHz and 20kHz, 3 times per second. We found an excellent test where both of these tones can be played to determine whether a person can detect this sound or not at https://www.audiocheck.net/audiotests_mosquito.php . Because these signals are at the upper limit of the normal range of human hearing in the mid HF Band, adults of a certain age, let's use over 30 as an example, normally wouldn't hear them.
We looked through current noise legislation and find nothing that would prohibit the use of these systems, though arguably there are ethical questions about a system that targets a particular demographic in such a invasive manner.
We recommend that you contact the Hawai'i State Dept of Health, Noise Branch, and ask if there is any State regulation governing the use of these systems. Their contact info is below. We would also appreciate your letting us know if you find more. For our part we will post your note (without identifying information) and our reply and ask our blog visitors if they have any information to share.
Phone: (808) 586-4700
Fax: (808) 586-5838
Hours: Monday – Friday 7:45am – 4:30pm (except for State holidays)
Jeffrey Eckerd, Program Manager (email@example.com)
We have also added you to distribution for noise and related info that we from time to time share.
NOTE TO OUR VISITORS: If you have any information to share regarding regulatory standards for this use of the Mosquito System please let us know using our Contact Form. Mahalo.