If you spend enough time browsing eBay to break down interesting electronic gadgets, you're sure to see suggestions for some questionable gadgets. This is how I recently became aware of these tiny GPS jammer that plug directly into an automotive 12v socket. Delivered to your doorstep for less than $ 10, it seemed like a perfect device to rip open in the name of science.
Now you may be wondering what legitimate uses such a device could have. As far as I know there aren't any. The only reason you'd want to interfere with GPS signals in and around a vehicle is when you're trying to get away with something that you shouldn't be doing. Perhaps you're driving a haunted company car and want a quick two-hour nap in a parking lot, or you might want to turn off the car's built-in GPS that you stole just long enough for you to take it to the car store. You know how to do it.
However, we are not going to delve into the potentially nefarious reasons this device exists. Hackers have never been too picky about the devices they investigate and experiment with, and there is no reason why we should start now. Instead, let's take this gray area hardware for a test drive and see what moves it.
Although the GPS constellation's average altitude of 20,200 km (12,550 miles) may not be quite as high as that of communications satellites in geosynchronous orbit, they are still quite a long way off. Given this incredible distance and the size of the antenna on most GPS equipped devices, it's no wonder the received signal is very weak. So weak, in fact, that it is generally below the noise floor. Only with clever algorithms and a dash of wizardry can your phone turn that whisper from the stars into something resembling useful information.
It is this fragility that makes these types of inexpensive signal jammer possible. It doesn't take much to overwhelm the legitimate signal. Remember, a device like this does not attempt to mimic a GPS satellite, but simply emits loud enough nonsense that the real satellite can no longer be heard.
When the jammer is on, we can clearly see how the already meager signal is absolutely wiped out by the patterns sent by the device.
There is just no competition. The legitimate signal is tens of thousands of miles away, and this thing is screaming its head within range. I haven't tested the range of this device, mainly because I didn't want it to be turned on for longer than necessary, but it is capable of doing the deed at least several meters.