So I've been attempting to build on of these boosters and found some interesting information. So on the white hat hacker forum (the one i'm on is invite only) there are a couple issues with using the unit. First you must have the transmitter within 5 - 7' of the fob when using high end equipment. The other end near the car. This being said they were telling me why the hell would anyone use this at someone's home??? It is designed basically to be a two party system. Couple out to dinner man in side or near them at the restaurant man out side in the parking lot. Keep in mind just the booster cannot start the car that is another signal in most models. Either way still attempting to get one sorted to test at home but thinking about it my X5 is in the garage first and my key is over 80' away in a kitchen. So don't think it is my worry but thought the idea was cool enough to figure out!!
With that note some older models use a single RF signature and other use revolving so you cannot simply copy one and do it at another time you must copy all. There is a bit more to this part but i'm still learning.