No, the Sprint Booster will not void your warranty. If concerned, the Sprint Booster can be removed before bringing it in for servicing, and they would never know it was on the car. They would not know it was there because it does not leave an electronic signature of any sort. You could leave it in if you want as many people do, but I would definitely turn off the Sprint Booster and remove the switch before taking it in for servicing to prevent "dealership blame" for any future issues.