Some say they do and others use different whistles. I've never seen them work ever. But I guess they do for certain uses.
Do Dog Whistles Really Work? | Canidae Blog
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Do those silent dog whistles really work on dogs?
They aren't really silent ... They're above the range of human hearing.
Most of them can actually be adjusted for frequency. Which is why some people think they don't work. Usually those people didn't read and/or follow the instructions.