Whoops. Can a mod {MI} that thing? Sorry.

Those ultrasonic things make me nuts. Supposedly humans can't hear them, but I guess I'm like a superhero or something. But to address your question: we just cleaned out my grandmother's apartment (she recently died) and found both a plugged in ultrasonic pest deterrent device and fresh mouse droppings. So, I don't think hers was working.

I have been using the ultrasonic things this week after the "try to plug up all of their holes with steel wool" didn't work so well. I can hear them which is a little annoying. Jury's still out on whether they're working. Apparently they only work sort of as if they were a light bulb [i.e the sounds only go where they're not blocked] so they do fuck-all for the inside of your cabinets and walls which is where mine are. That said, I was surprised 1. how easy it was to move the stove and the fridge to peer behind them [and I am not so large] and 2. that they were NOT getting in from behind either of those appliances. That said, I have no idea where they ARE getting in and I'm running out of steel wool!

Borrowing or permanently acquiring a cat would probably get rid of them- is this possible? Even if the cat is a useless mouser, the smell of a cat is a good deterrent.

Maybe a friend has a cat and a brush full of cat hair? I'd give sprinkling the cat hair around a try.

Hmmm. Maybe the ultrasonic is worth a try. Can't hurt. I'll try to get behind the fridge/stove too.

Alas, I am leaving the country soon for 3 months otherwise I would get a cat.

We live in a very woodsy area and we have mice in our attic/crawl space. Um, we use poison on them. I guess it's not so nice but it works, at least for awhile. They eat it and they die, and the good part is, it makes them thirsty so they go outside to die (usually but not always). For awhile there will be no mice and then new ones hear about the vacancy on the rodent Craigslist and they move in. See above, repeat. We've had the professionals out here a few times to plug up holes but the critters still get in.

We put several of the ultrasonic things up there and for us they had no effect at all. We found droppings right by the ultrasonic units. The mice were taunting us. We could sense them giving us the middle claw from their paws.

I do feel a tiny bit bad about it. But they cause a lot of damage to the insulation. They don't clean up after themselves. They belong outside. To quote Macauley Culkin, of Home Alone: "This is MY house and I have to protect it!"

So yeah, poison.

(ducks head, slinks away)

1858 houses have lots of holes. After many years and different approaches we stick with the tried and true -- standard spring traps baited with peanut butter. If you're not skeeved out by dropping them in the trash you can probably handle using a pliers to release the buggers into the toilet bowl and rinse and reuse the trap (most times). Not that they're expensive.

Back when I lived out in the sticks, when I got mice I found that a vigorous program of (lethal) trapping worked well. It took a couple of weeks to kill several wee mousies, and then there were no more dead mice or signs of mice. The house stayed mousefree for at like six months to a year.

I felt bad about killing the wee mousies. Then a wee mousie decided that it really ought to climb on the clean dishes in the dish drainer, even though they were clean and had no food upon them, and display its displeasure at the lack of food by pooping on the clean dishes in the dish drainer. After that it was just FOAD.

If you have a mouse that isn't killed by the trap, slide the mouse + trap into a bucket and gas it with car exhaust. Death is VERY quick.

Yeah, I am using the plastic traps from Victor which seem to work quite well...except there was one mouse caught and not dead. Scared the heck out of me when I picked it up and I saw his little face inside. I drowned him quickly. Took one or two seconds. Terrible. Don't know how long he was caught there.

I also have a live-trap, all metal thing. There is one in it right now, looking scared. I am making my housemate deal with it, i.e. take over to behind a big old church or kill it.

So yeah, poison.
(ducks head, slinks away)
Yeah, me too. We have periodic problems with not only mice, but rats as well (mostly in winter). I take the same approach as I do to spiders and other nasties - the outside world belongs to them and I leave them alone. Inside the walls of my castle is another story and I will stop at nothing to protect my territory. It's really no more than they would do to us if they had the chance (that's my justification and I'm sticking to it). Spring traps baited with peanut butter work well for mice, but rats are smarter and we use those chew-through bags of poison in copious quantities at the first sign of them.

Yeah, unfortunately, if you have a mouse problem, you really have to get medieval on them in order to solve it. Traps and poison, I'm afraid. You could go with a cat in the living space and traps/poison in the attic, crawlspaces, etc (i.e. everywhere else the cat can't reach.)

Sometimes, though, you can get saddled with the cat that prefers to play with the little buggers, instead of exercising her license to kill.

And you will still need to plug the access points, or this will become a regular problem.

If you have rats, and not mice, you might want to call in a professional exterminator. Rats are a whole different problem, and dangerous, to boot.