Personally if they don't know you then it isn't likely that they are going to try and steal the car. Its to much work for a common criminal. All they look for is a quick fix. I've lost an alarm remote and I didn't have my alarm taken out because of it. I would't worry about it if you feel that the mugger doesn't frequent the area or knows you license plates number. If he has your dads drivers licenses, then he knows the address and on just that I would get everything changed, and of course if you aren't able to find that spare then you will have to get it rekeyed anyway.
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