Mine has worked well for many years. One Spring I counted 23 of them that entered over the Winter.
I also use dryer sheets but I've found droppings on them, so they didn't do the job.
Fresh Cab seems to work well for the inside of the car. I've never found any traces inside a car when using that. If you open the door and you can't smell it, then it's time to change it with a new one. It smells nice.

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Put a big hunk of 0000 steel wool in a zip lock baggie and shove it in your exhaust pipe(s). The mice will chew through the baggie but stop at the steel wool. The baggie contains the wool so it is easy to remove from the pipe(s). Just don't forget to remove them before you start the car.

What's "fresh cab"?

Around here it's sold at Tractor Supply stores. Small bags of loose herbs that have a very pleasant smell, but mice hate it.

Verne