Mice come in when it gets colder out. Some stay and some leave when the weather gets warm. I have one of the electronic thingys you plug into the wall outlet and have been "mouse free" for over a year now. It also kept the ants out all year. That in itself is a blessing. I forgot to mention all of the flea trap thing. You take a shallow white bowl, put water and a little dish detergent in it, and suspend a night light over the bowl at night. Really works if you have a
problem with them.