That is the question raised by the incoming Chair and Ranking Member of the Senate Judiciary Committee in response to FBI assertions that the agency is entitled to use a device masquerading as a cell-phone tower to intercept your calls and texts in public.
The Daily Dot explains the troubling technology at issue:
The Stingray is a wireless wiretapping device—generically known as an IMSI catcher [international mobile subscriber identity]—which, while masquerading as a cell-phone tower and transmitting intermittent signals, can deceive a mobile device to force a connection. Once this link is established, the data collected by the Stingray can be used to ascertain the identity of cell phone user, along with who, when, and to which numbers a call is placed. Further, the devices can be used to capture content, recording phone conversations, and even snatch SMS text messages.
Read more here about the FBI's use of this technology and the debate over whether it needs a warrant to do so.