Does anyone have experience with a mouse *inside* your walls

Put traps in your attic. They’re following electric wires into the walls.

So sorry.  I grew up in a rural woodsy area and always had mice around.  What you don’t want to happen, if you can help it, is for it to die inside the walls.  

I have never heard of drilling holes. Our walls would have looked like Swiss cheese. 😄 🤷‍♀️  If it got in it will get out. I have watched a mouse fit through an inch or less opening under a door.  It does not take a big opening.  

 Look to see if you have areas where pipes and such go out, where you have gaps or holes in a closet or around baseboards, or anywhere they can get it and try a plug them. They are looking for food so don’t give them a source.  Keep things in containers and no open food on the counter.  

Sorry I really don’t have any advice as we just trapped when we could but it was all part of living where we were. Hopefully someone can give you some good advice.

For my MIl, it was the opposite.  They could get into the stone foundation of her basement easily, and then they followed water pipes through the walls.  

So if you have a basement, you may want to check out that area as well. 

Call an exterminator. We once had one get into our walls on the first floor through some conduit in the garage. The exterminator located the access point, blocked it (since the mouse was not in the walls at the time), and put traps near the access point in case it came back.

Theoretically, we could have done it ourselves, but I felt more comfortable knowing a pro had fully examined everything and eliminated future issues.

Mice can slip through a hole the width of a pencil -- you're never going to be able to seal your entire house from them. They love to follow the water pipes into all areas of the house.

Your best bet is to set out half a dozen (or even 10) traps at the same time with various baits. If you have one mouse, you have a dozen. You need to trap them all within a short time before they have more babies. Keep it up for 3 weeks or so, or until you stop trapping any.

If you call an exterminator, they generally use an anticoagulant chemical bait. Those chemicals can be toxic to the wildlife that may eat the mice after they are poisoned and leave the house.

Can you tell I've had to deal with this before?

We didn’t, but our neighbors at the lake did. Every spring when they opened up for the season they would smell a foul smell in their kitchen. They thought initially it was coming from the kitchen drain or something similar. As the months progressed, the smell would lessen and eventually go away. When they decided they were going to completely redo their kitchen, they ripped down all the tile and sheet rock on the walls and found a nasty surprise. There were HUNDREDS of mouse skeletons inside that wall! Apparently there was a piece of old, empty conduit running through the studs inside the wall. Every fall, the mice would get in on one side, run through the conduit and fall down into the open space between the studs on the other end where they couldn’t get out and they would die in there. 😱😱😱 🤮🤮🤮 So every spring it would stink because of the new additions to the pile. 

I would go looking for places they can enter either in the attic or in the basement and set your baited traps there and hopefully you’ll get them before they die inside the walls. It doesn’t take a huge hole for them to get in, I’ve read a hole the diameter of a pencil is all they need, so be thorough in your search. From my personal experience, I’m just going to say there is never just one mouse. If you have evidence of one, in all honesty you probably actually have 6-10. Wishing you luck, mice suck.

My mother also plugs in those ultrasonic mouse repellent gadgets. I can faintly hear them when I stay overnight. It seems to work.

My parents had this going on last year. They had a company come in to trap them and then seal up holes. They put traps in the basement and attic and were catching plenty of them.

Be very careful what you do about bats. Investigate what is legal to do before you do it or allow an exterminator to do anything on your property. Several bat species are protected.

I’m pretty sure you can’t kill most bats. I had this issue at work and they had to wait for the bats to voluntarily leave, then plug the places they are getting in. You can only plug the entry points at specific times during the year too. You can not bait, or trap, or kill most bats. So it’s really limited what you can do about them. Here most ‘regular’ exterminators won’t deal with bats you need a bat specialist. However, bats do respond to electronic bat repellents and it is pretty easy to discourage them from roosting if those devices are legal in your area, BUT installing those might also be limited to a specific time of year depending on what species the bats are.

Honestly, I would call an exterminator. If there's one, then the likelyhood of more is great. And you sure don't want them dying inside the walls or in your attic.