[evgen]

Phone jammers are illegal because they are broadcasting into regulated spectrum. There is no such spectrum regulation around audio transmissions. I will not say one way or another if this device actually works as adertised, but particularly if the signal is outside the range normally audible to people there should be nothing illegal about this device.

[caminante]

You're right about FCC laws, but there are non-FCC laws, too, such as penalties for willful interference with federal/state emergency communications.

I'm wondering if this device would cause issues for a nearby person's emergency communications. Seems potentially really bad.

[NetMageSCW]

You seem to be pearl clutching a bit too hard. I am positive there are no legal issues.

[caminante]

It's not "pearl clutching" when there are enforceable laws like 18 U.S.C. § 1362.[0]

Were you even aware of this?

Can you actually cite a legal opinion about the device or similar applications? Otherwise, I'm assuming you are speculating, too.

[0] https://www.law.cornell.edu/uscode/text/18/1362