Police are using a new tool called Stingray, which is a mobile device that masquerades as a cell phone tower and is usually installed in a police van. Your phone is constantly seeking the closest tower, even when you are not making a call. As a police van nears your location (using Stingray) your phone connects and automatically routes data through Stingray just as if it was connecting to a normal cell tower. The data can be displayed on a laptop computer within the van, allowing officers the ability to view the information. It is then passed on to the closest cell tower so your service is not interrupted. Police can get identification and telephone numbers, the numbers you might be calling or texting, and of course your location.

More information: http://www.usatoday.com/videos/tech/personal/technologylive/2015/08/24/32131267/