Watch Dogs

Police scans are initiated when a citizen witnesses a crime and calls the police. Before they send the cops after you they will scan the area to locate you. You will see yellow circles on your mini map and all you need to do is exit the circles. Yellow circles will keep popping up and you'll need to keep moving. Next to your wanted level is a percent and if that reaches 100%, the cops will be on you. If you stay out of the circles long enough, you will successfully escape the scan.

There is one item that will help you out greatly i.e the Jam Coms. You can craft these at will if you have the materials and have purchased that from the crafting skill tree. Make sure to have it selected by holding and selecting it from the weapon wheel. To use it, hit If you use it while in range of the police scanner, it will temporarily turn the circles white and give you a few precious moments to get out of range. You may need to use more than one to escape the scan.

A really simple way to farm this is to jump on the highway with a fast performance car. Cause a little mischief that will result in the cops being called. Once someone starts dialling the police, hop in your car and just keep driving down the highway at high speed. If you start on the highway at the north end of Mad Mile, and head East as the road will turn South past past Navy Pier, you should escape the scan just as you cross the bridge going into Brandon Docks. No Jam Coms will be needed, provided you avoid accidents. Now cause the police to be called once again and head the opposite way, rinse and repeat until you have the trophy.