Thanks very much for your reply Mr Steam, it is probably helpful if I knew more about this sort of stuff. But I also may not have explained what I want clearly enough.
When you say something is in my bedroom and something has USB power I think it’s not what I want, so I’ll clarify.
I want this whole thing to be outside at the dog yard. I don’t want to be disturbed at all.
I have 240V (Australian mains) power to there (not under cover, but could make a protective box), alternatively a variety of battery options (12V car batteries charged via solar panel ; 6V torch lantern batteries, 9V little rectangular batteries). But no spare computer to put out there providing USB power - however, could I just plug a powered USB hub to the mains power and then hook the USB power bit to it? i.e. if all it is doing is providing power, does a powered hub really need a computer?
Once I know the sound (e.g. buzzer) the set up can make I would manually use it to train my dogs to be quiet and go to bed when they hear it. When they understand that, then I will set it up in the dog yard so that if they start to bark at night the sensor hears it and makes the sound (buzzer) work, they hear the buzzer and go to bed. And I don’t have to go out and tell them to go to bed.
AS AN ALTERNATIVE or extra - instead of/as well as the buzzer, can the circuit turn on a tap to make a sprinkler work?
How loud is the buzzer? It does not need to be siren loud, but loud enough some barking dogs will hear it from about 10 metres away.
thanks you, I very much appreciate your help.