This is for my residence. Living up in the mountains of Colorado, mice are just a thing you deal with. And I'm usually able to keep on top of them with just the sticky traps. But they seem especially plentiful this year. I cleaned out the furnace room today, which is where they tend to congregate, but that room has an opening between the floor joists, where I am sure they are still living. We can sometimes hear them in the walls, and they certainly leave their tracks in various places.

So, I want to get rid of them, but I cannot get to the area under the joists. I am ready to call an exterminator. Just wondering your experiences. And what type of treatment? Is this a thing where they will need to do some sort of fog poison, and we leave the house for 3 days (I'm thinking Seinfeld episode - anybody play Risk? I am attacking the Ukraine!)

Or are there other treatments that I can expect them to use? If all they are going to do is set traps, well, i can do that. I'm expecting that if I pay somebody, they'll do something more than I can do, and be positive that they get rid of all of the mice in the house.

And I thought you were talking about a kitty cat. Mine likes to sit on top of the hanging, high efficiency boiler and watch the sill plate. Spends the evening and mornings there. Does a good job of catching them too. She also likes the stairs under the bilco door.

So if the exterminator came and set off a fog poison to kill them in the walls, what do you think the place is going to smell like in a week?

Traps, lots of them. Back to back, anywhere you can reach. I like to bait with peanut butter with a small piece of cat kibble in it. Trying to get the kibble out sets the trap off. Use the old fashion snap traps, the new spring set ones, mix and match. We even take one end of the soffit off outside and set traps there. You can also set out bait, but i try to avoid that.

If you can't get under the openings then make a framed in 1/4" galvanized mesh screen to cover any opening from the side you can access. One of my tenants left their garage open and a family of mice took up residency. They had so much junk inside the garage. My tenants only told me about this when the mice/rats started to destroy their belongings. So when I came by, again the garage was left open. I told them there is no use having me set traps if they are going to keep they stuff in cardboard boxes, instead of sealed plastic tote bins.

my PRO uses bait traps

that way he can see if there is any activity

I've never had much luck with any kind of trap for an infestation. Bait to kill. Yes there may be a smell for 2-3 days but it is highly effective and the problem is taken care of quickly. I use sticky traps to catch them before it gets out of hand, but never had luck for more than that. As others have said, you have to close up the holes with steel wool, screen, or similar to keep them out or you will have more friends join the party. It's getting cold outside so they are looking for a place to winter.

Martin - go to a Tractor Supply Store or Farm Store. Get a big bucket of the mouse/rat bait.

Put it everywhere (in the furnace room, where the floor joists are open, etc) and behind your fridge, stove and in the attic, … everywhere

You can get the same stuff at HD, Lowes, etc (it's call TomCat) but they only sell the small bags ... if you think you have an infestation then get the bucket. You can get it on line too - but it's usually at the farm stores easy enough. Right now I wouldn't be surprised it's on sale since "it's the season".