As a sceptic and electonic engineer (with mice in the walls and loft), I reluctantly bought a set of ultrasonic mice scarers not expecting much to happen. Needless to say after 2 weeks, the little blighters are taking no notice at all.
As they remainin 99% of the time inside the wall and internal floor cavities, I can't get at them. It's not surprising the ultrasonics do no good since that stuff won't penetrate building materials or even insulation quilt. Managed to get two by mousetrap in the roof joist spaces, but they are mostly taking no notice.
There are some other fangled gadgets which modulate the mains wiring with RF. I am even more sceptical about these, but they claim to get round the problem of ultrasound not going through stuff. Quite why mice would get upset by some weak RF fields has never been explained. Methinks it's more pseudo-science. Has anyone ever made these things work?
Otherwise it's poison, but I'd sooner not have too many rotting mice in the ceilings. There are no holes anywhere (ie I haven't a clue where the external hole is to block up, because there is nothing obvous left to block), so keeping them out isn't so easy.
