I unfortunately know about mice problems, and my parents have had a whole family of rats infesting a small, old stable at their house in the country. The bastards are difficult to catch or kill, and they are smart. Like: scary level smart!
That said, I just killed a mouse on the stairs of our building two evenings ago. I stomped it with my slipper. Needless to say I threw the slippers away.
In the past I have tried traps, both the sticky ones and the more "humane", plastic ones that don't kill them. The sticky traps worked for the first two mice, then the others understood how it worked and avoided them, simple as that.
Then I decided that the only way to make sure you are rid of them is to actually block all possible access points to the flat. So I spent two days on my hands and knees, stuffing all holes and crevices along the walls with steel wool. They can't chew through it and they stay away because its small steel strands can potentially hurt their eyes.
It took some time and a lot of hard work but I can now say that I haven't had a mouse in the apartment for months (knock on wood, cross fingers, etc.).
I do have a lovely CO2 gun, It's a
WinGun Sport 705, but I have to say I mostly use it to scare away (and hopefully hurt a bit...) the pigeons that like to poo all over my kitchen window sill. It works like a charm.
