Finding a dead rodent in your walls is challenging. Unfortunately, even with all the technology out there, the only real way to find it is with a strong sense of smell. You can recruit a dog or cat to help pinpoint the area for you. You can sidestep the entire problem by avoiding poisons that are ingested by rodents that then hide in your walls to die. Another preventive step is to seal your food and to plug gaps between your living space and the side of your walls.
Things You'll Need
Strong sense of smell
Rodent removal company
Use your nose to find the dead rodent. The only way to really track down a dead mouse or rat in the wall is to smell it. Once pinpinted, you can cut a hole in the drywall and remove it.
Bring your dog, or a neighbor's, indoors and set it loose. The dog should naturally gravitate to the smell to investigate and alert you by whining or scratching at the area. A dog may identify only the general area of a dead mouse but not it's exact location. Once you have any idea where it is, pinpoint by using your own nose.
Find a cat that has an affinity for mousing. Not all cats will necessarily go for a mouse, especially an older cat. A cat who enjoys hunting will seek out the area. Watch the cat to see if it circles an area, smells the wall or paws at it. As in Step 2, use your own nose to pinpoint the exact location.
Wait it out. The smell should dissipate within one to two weeks or longer for a larger rodent. Use deodorizers and plug up any holes inside and outside your home so other animals won't venture into the wall to investigate.
Hire a rodent removal company or exterminator to investigate. They will most likely need to cut a large hole in the wall to find and remove the dead animal.
Keep your food sealed, walls plugged and your home clean to avoid rodent issues.
A mouse or rat that eats poison will usually hide in a wall or ceiling to die.