Wireless Car Locks are designed for convenience.  Yours, and also car thieves'.

In this NYT story, the author describes why he now keeps his car keys in the freezer:

He explained it like this: In a normal scenario, when you walk up to a car with a keyless entry and try the door handle, the car wirelessly calls out for your key so you don’t have to press any buttons to get inside. If the key calls back, the door unlocks. But the keyless system is capable of searching for a key only within a couple of feet. 
Mr. Danev said that when the teenage girl turned on her device, it amplified the distance that the car can search, which then allowed my car to talk to my key, which happened to be sitting about 50 feet away, on the kitchen counter. And just like that, open sesame.

He's now using the freezer as a Faraday cage to prevent this - his Prius had been broken into three times as of the writing.  This method is less useful for stealing the car than for entering it, because once it's driven away there will be obvious difficulties without the key.

I think my plan will involve two things, none of them below room temperature.  One, we will no longer keep ANYTHING of value in the car.  And two, we will get Faraday bags similar to those that protect your new "secure" passports and keep our key fobs in there when not driving.