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I use a faraday pouch,it works a treat even when standing next to the car,I suppose like anything the quality of the pouches can vary.
Perhaps I live in a low crime area (perhaps not?) but I don't give it much thought. I haven't looked into specifically how a thief can boost a key signal and steal my car, but I have tried unlocking/locking the car with the fob a few feet away and it doesn't do it. Therefore my keys sit on the same shelf all my other car keys have sat over the years. I do have gap insurance tho, so if it does get nicked I'll (hopefully) get a replacement.
A very easy way to make a faraday case, tear off a foot of aluminium foil fold it twice, fold your keys in it, job done, try it.This works.