Sahas Katta has dozens of apps on his phone, including one called "My Tracks," which keeps tabs on how far and how fast you drive.
The University of California, Davis student was ticketed recently for doing 40 mph in a 25 mph zone.
He says he never speeds and was pretty sure the radar gun was wrong.
It just so happened that the app had been running at the time, and it indicated Katta never got above 26 mph. So he printed out all the data, and took it to court. The judge was impressed.
"I think the evidence I presented was very new and refreshing, and it is cutting-edge technology. Clearly, this had not come up in his court before, which is why he made a statement afterward declaring me not guilty," said Katta.
It probably also helped that in court, the police officer could not remember when his radar gun had last been calibrated.