On Friday, November 4, 2016 at 1:27:22 PM UTC-7, Ben Coleman wrote:
Good to hear these gizmos work, this is one of the proposals for our club (using a mix of ultrasonic and audible sounds including distress and predator sounds).
Regards Ben

The electronic noisemakers were thought of as "most people cannot hear" or "all you hear is an intermittent clicking noise".
It's not as bad as the Ludovico treatment*, but probably best to turn the thing off when people are around unless they're deaf in one ear and can't hear out the other.
Jim

* from "A Clockwork Orange"