The mice hate it.
I live in the country with fields and woods around my house, every winter little uninvited guests moved in, I guess for the warmth, it was not uncommon for me to sit watch TV and one would run across the floor.
Over 5 years I tried everything traps which I hated being a animal lover, they had to go after I heard screaming one night when it caught a mouse but only by its nose, causing me to have to stop the poor thing suffering, I did not enjoy that at all.
Next I tried the humane traps in one winter they caught a big zero, so it was on to poisons with some success but it was never 100% and it seemed by half way through the winter they learned not to touch it, plus it was a problem because of my pets.
After 5 years I came across the sonic mouse repeller got home plugged it in and hoped, the first night I did see a mouse but after leaving it on for 3 days no more mice.
I have now had it 3 years, It gets plugged in at the first sign of cold weather and stays on 24 hours a day, I have not seen heard or found any signs of mice in 3 years.
I had a friend that moved abroad that in formed me she was loving her life there apart from the fact they had rats kept getting in the house and had huge rats in the garden, I sent her one of these thinking it would just keep them out of the house, but she has informed me it seems to have got rid of them from the garden as well.
Recommended to anyone with a rodent problem.