A meaningful debate is starting to brew about law enforcement's use of commercially available cell phone data for purposes of criminal investigations across the country. 

The data, called open-source intelligence by those who advocate for it, used to only be prepared and sold by brokers, generally to marketers and advertisers.

Information is sent daily from "phones, cars and other connected devices" to commercial brokers, The Wall Street Journal wrote this week. That data is then widely used in "finance, real-estate planning and advertising".

But recently, these brokers have created products specifically for law enforcement. The products have "increasingly been used to screen airline passengers, find and track criminal suspects, and enforce immigration and counterterrorism laws," according to the Wall Street Journal. 

Agencies that are using the data, or considering use of the data, include the Department of Homeland Security, the Internal Revenue Service and the FBI. 

Skeptics of the practice see it as akin to warrantless searches, with the Journal characterizing the practice as an "end run around the constitutional guarantees against unlawful warrantless searches".