They can clone a key fob pretty easily if they take possession of it (test drive) or capture the signal with a transponder from the car or the keys sitting inside a building, then duplicate a fob if they have the right software and or access to the database the locksmiths and dealerships have. Newer vehicles have rolling encryption keys, so the fobs can't be cloned as easily as older static keys...but its only a matter of time before a bad actor figures out a solution.