I have had experience with ultrasonic rodent deterrents and they seem to
have minimal effect.  The mice either get used to it or move a short
distance away.  You'd probably have to have a dozen of them to actually
keep mice away.

I prefer little Havahart mouse traps which catch the mouse alive.  I
deposit the mice in a natural setting several miles away.  There are
also revolving-door type traps which catch several at once, except
sometimes the door squashes the mouse.

H.V. Taves • Southern Forest Heritage Museum • Long Leaf, LA 71448