An app called Lookout has hunted down a woman thief who stole a smartphone from a woman's car in Florida.
The app detects when someone is trying to unlock a stolen device and snaps pictures of the thief.
The app also emailed the woman maps of the location where the phone was last used, media reports said.
Cathy Carter from Florida's Lakeland area went to see her doctor and left the front window of her car open.
She forgot the phone on the seat which was stolen by the time she came back.
A few hour later, Carter received an email with a picture of a woman and a map indicating where her phone was last seen.
She posted the thief's pictures on social media and one of Carter's friends recognised the thief who was later arrested.