I've had two different ones over the years, both ran on 9 volts.Does it use 9v or a pair of AA ?
I would imagine it’s omnidirectional and is at the high end of the hearing scale, so is making noise in a mostly un-occupied frequency range.
( I have a vivid imagination some times )
If it doesn’t run 5 or 12 volts you would need to put a little transformer in the circuit to put it parallel to the horn...
Oh, one possible situation could turn ugly: encountering an angry, deaf dog