At what point would you consider the attentions of the powers that be to breach your privacy?

How about discovering that your car had been fitted with a GPS vehicle tracker without your knowledge?

That's what happened to a young Californian man known only as Greg, according to Wired. The 25-year-old San Jose resident found one on his Volvo SUV, and after telling Wired about it, discovered a different one shortly after. His girlfriend's car also appears to have been the subject of suspicious attention, according to a witness.

GPS trackers are becoming increasinly prevalent as a crime-fighting tool, but it also means that anyone whose car is fitted with such a device could be subject to around-the-clock surveillance - whether they're connected to a crime or not.

Greg's case is just one of several such incidents of vehicle tracking. He suspects he might be under watch because his cousin may have been involved in the Mexican drugs trade, and the car used to belong to him.

Regardless of involvement in any crime, it appears alarmingly easy to attach a tracker to a vehicle. With magnets, it may only take a few seconds and if placed in the right area could remain undetected for months. Greg only noticed his because a radio antenna was slightly visible beneath his vehicle.

The legality of using these devices without a warrant is currently being debated at the Supreme Court.

In the meantime, just be aware that this time, Big Brother really could be watching you.