Rats and mice nesting under the hood of the car can do an astonishing amount of damage. Especially when they gnaw through the electrical harness just underneath the hood of most cars, a single broken wire can take hours to locate and cost a great deal to repair. Of course, chomping into the wires for throttle sensor is bad enough.
When you are using an ultrasonic device to rid your residence of rats and mice, it’s important to use it to “herd” the rodents inside out. You place the device in the room farthest from a outside, door, and then move it closer and closer to the door, eventually driving your pestiferous little visitors outside.
When you are protecting a car in your driveway, you apply a similar principle. As long as rats and mice aren’t nesting under the hood (or in the drive train, in the trunk, or in the interior of your car), you don’t really care where they go, assuming you have taken other protective measures for your house. Ideally, you would place an ultrasonic unit on the ground directly under the engine of your car, but then there is the issue of weather. It’s precisely rainy or cold or winter weather that drives rats and mice to the cozy warmth of your car, the same weather that interferes with the operation of your ultrasonic unit.
That’s why the solution is for outdoor cars is not ultrasound. It’s clean up. Make sure that any rats or mice have to make a long run (for a rodent) across unprotected territory before they reach the refuge of your car. Make sure the grass in your yard alongside your driveway is kept short. Don’t let clutter or trash accumulate. Don’t grow any kind of creeping plant along your drive. They create caverns of safety for rats and mice, and they even catch food blowing in the wind. If your landscape feeds the animals, then they just want to go to your car for shelter. But if there isn’t anything to eat, they will move on.
Poisons just don’t work in the driveway, especially if there are dogs and cats roaming across your driveway.
As for your neighborhood dogs and cats, please consider this. Fans and belts under the hood can trap, mutilate, and kill pets. Just as you don’t want rodents under your hood, you don’t want your neighbors’ pets under or in your car either. If you park outdoors, you may not always keep the neighbor’s cat from sleeping under your hood, but you can make a habit of giving your hood a good thump, or waiting just a moment after you close your door before you turn the ignition key, to give pets a chance to get out of the way of moving parts.