WASHINGTON (AP) — Like almost everyone else in America, thieves tend to carry their cellphones with them to work.

When they use their phones on the job, police find it easier to do their jobs. They can get cellphone tower records that help place suspects in the vicinity of crimes, and they do so thousands of times a year.

Activists across the political spectrum, media organizations and technology experts are among those arguing that it is altogether too easy for authorities to learn revealing details of Americans' lives merely by examining records kept by Verizon, T-Mobile and other cellphone...