Getting rid of mice can be difficult, but getting rid of the smell if they die inside your walls is more difficult. This usually happens when the mice are poisoned with a warfarin-based toxin. The smell of a decaying carcase is potent and can last from several days to several weeks, depending on the rate of decay. There are ways to speed up the rate of decay and to remove much of the odour more quickly than Mother Nature.
Remove the dead mouse. The quickest and easiest way to get rid of the smell is to remove it. If the carcase is in an easily reached area, put on the rubber gloves and face mask and remove the body. The smell with go with it, but expect there to be a slight lingering odour for a few hours. There is a real possibility that you will not be able to find the carcase to remove it. In this case, other measures will need to be used.
Place activated charcoal in the areas where the smell is the strongest. Activated charcoal is a natural odour absorber. If you are unable to locate the dead animal, but you can pinpoint the areas of strongest smell, cut a small hole in the wall and place the odour absorber into that area. Keep in mind that dead animal odours can be tricky. Air circulation plays a big part in where a homeowner smells an odour and where it is actually originating. Also, only homeowners who are willing to repair the drywall damage themselves or pay for repairs should cut holes into their walls.
Place pans of unbrewed coffee grounds around your home. Coffee grounds are also a good natural odour absorber. Since coffee grounds are non-toxic, they can be placed around the home in the open. Strategically place boxes in the attic, basement, air conditioner intake vents and air conditioner vents.
The trick to getting rid of the odour as quickly as possible is to remove the source. If the carcase can't be located, the idea is to get the body dried out as soon as possible. As long as the body is wet, the smell will continue. Keep your home as warm as possible to help speed the decay process while employing the tricks above.
Never remove the body of a dead mouse without wearing the proper protective gear. Mice can harbour diseases from the plague to hantavirus, both of which can be transmitted to humans.