Most often when people engage in small crime, they are not engaging in smart behavior overall. Having phone with them is just one of multiple stupid decisions that were done that week. They are used to have smartphones with them all the time, so they do not think about them at all.
Another pretty common way of catching you is that you brag to friends or family about the crime and one of them tells the cops.
Accepted, that's the stupid class. And no doubt such detection would be very useful in solving serious but unintended crime such as a hit-and-run accident.
Another pretty common way of catching you is that you brag to friends or family about the crime and one of them tells the cops.