Car radio jammer , car black box jammer
If you noticed that your parents are tracking you when you are at school, then they probably used tracking technology granted by Verizon or something similar. In short this technology allows them to create something like a perimeter around your school, area around the house or any other particular territory between cell phone towers. Then they will use mixed GSM/GPS technology to track you down inside the perimeter.
To get rid of such annoying tracking you can use GSM/GPS jammers which will protect you in your school and other places from this type of location tracking. When you use this device to avoid being tracked your parents will see that you are free personality and your claim for independence is serious!
By the way, you can use this jamming device for other purposes like to stop blabbing cell phone user around you or disable GPS tracker in your car. And don’t forget that if you have some additional questions - you can ask them anytime! ;)