I agree with Tringa and trapping seems your best option if it is mice.
Never seen any proof that the electronic sound emitting devices work
I rented a flat above a shop on the edge of Nottingham in a three storey Victoran building a few years back which became over-run with house mice like all the buildings in the row. I made certain they could not get any food and kept everything out of their way in secure cupboards and freezers but they still came and seemed to enjoy eating floorboards!!!. The local pest control unit decided to lay poison down in a nieghbours flat that was also getting them very badly but a few weeks later everyone in the row had flats that smelled of rotting dead mice, it really was horrible.
The course of this infestation may have been down to a pet shop owner in the row who used to sweep all of his cage bird mess into the back of his yard and still does. The mice came back and in the end i resorted to the old fashioned trap before i had enough money to move (even though i dont like killing for the sake of it). From what i can gather they still have a severe mouse problem and two of the shops are now takeaways and for some reason i never feel the urge to buy anything from them
