Question
We have been bothered by a rat infestation in our house, and  would like your advice on the use of ultrasound repellers.  In your opinion are they an effective way of controlling these pests?

Answer
Ultrasonics, according the research, have the excellent effect of separating good willed people from their money. Even the animal rights protest industry group known as the Humane Society of the U.S. does not endorse such products because, they know they don't work.

Please forgive my contempt for these devices. But I am glad that you asked before you wasted your money.  
If you want to learn what actually works in controlling rats, visit http://icwdm.org   

Remember, there is no magic in animal damage control despite what the hucksters say. that includes anyone telling you to spray this or that to "drive the rats away".  If it sounds too easy, I can assure you it won't work.