Please let your readers know that GPS jammers are illegal to own, operate, and market in the United States. Here is a link to the FCC
consumer alert on GPS jammers.
While I can understand that someone could make the personal decision that their personal privacy justifies blocking GPS tracking, please be aware that these GPS jammers are very effective and can jam an area up to a mile in diameter .
There was well-publicized incident of a personal GPS jammer that shut down the aircraft landing aid at the Newark, New Jersey airport. And there are documented cases of organized crime using GPS jammers in Europe  to hide their theft of high-value cargo trucks. Due to these incidents, and other reasons, the government  is actively pursuing effective GPS-jammer locator systems .
I would propose to you and your readers to consider the risks before considering such a device. While it may make a great plot device for a novel, I would not personally own one.
Respectfully, – S.G. in Virginia