To go back to the original question of whether key and car can talk to each other if 20 feet apart, is the answer to leave the key in the house and go to the car and try to enter it. If the door won't open then it means that the key is out of direct range.
However, there's also the question, which people have addressed, of whether the vehicle is safe from a relay attack. However, this may not be a worry in NZ where crime rates are lower than UK.