Straight Dope on Traffic Light Sensors

[Alan_nc]

Same principle as putting a blade of grass between your thumbs and blowing across it.  This one is housed in a plastic case usually about 1 1/2 x 1 1/2" and has a peel and stick area to attach it.  The wind goes across it as you drive and it whistles.  The sound is at a decibel level that humans can't hear.

Where I live most auto parts stores sell them, usually for under $2.00.

[Janx101]

In Aussie land too! .. but people fit them for kangaroo scaring..... or go all upmarket and get
https://www.shuroo.com.au/

With varying degrees of success. ...

Only 100% effective stopper of kangaroos I have seen on most roads is a semi trailer or road train

[hInstance]

$500+ !!!! That's a lot of money!