Anyone with $300 can buy a GPS tracking device no bigger than a cigarette pack, attach it to a car without the driver’s knowledge, and watch the vehicle’s travels and stops — at home on your laptop. Uses include monitoring teenage children, Alzheimer’s patients, and spouses.

However, the Supreme Court held on Jan 23 that under the Fourth Amendment of the Constitution, by placing a GPS tracker on a vehicle, a police officer is doing a search. Use of GPS trackers are illegal in California and Texas, and increasingly being cited in cases of criminal stalking and civil violations of privacy.