I own the exact same unit as the one you purchased and it's VERY selective as to what RFID tags can be used with it. Though I'm not 100% positive I'll say you cannot use an active RFID tag, I've not been able to get the two to work together. knowing of your other project I'd like to ask the question are you sure you need it? Once the RFID tag has been interrogated and accepted you can forget about it, can't you? You authenticate yourself, start a timer in your 18f1320 and it gives you a predetermined amount of time to either start your car, get in or whatever else you should choose. If the time period has lapsed then it can set a DeAuth bit and make you ReAuth to perform said action. If your car is already running nothing more need be done, if you and the running car are somehow parted you have bigger issues to deal with.