The Justice De­part­ment said Thursday it will re­quire its law-en­force­ment agents to get a war­rant be­fore us­ing tech­no­logy that tracks the loc­a­tion of cellphone users by pos­ing as cell­phone towers.

The cellphone-track­ing tech­no­logy, which sweeps up identi­fy­ing in­form­a­tion from every mo­bile device with­in range in or­der to find a tar­get device’s loc­a­tion, has been met with cri­ti­cism from pri­vacy ad­voc­ates who have raised con­cerns about the wide­spread data col­lec­tion it makes pos­sible.

Some­times called Stin­grays after a pop­u­lar mod­el used by law en­force­ment, the cell-site sim­u­lat­ors op­er­ate by mimick­ing a cell­phone tower and es­tab­lish­ing connec­tions with nearby devices search­ing for a cell sig­nal. When devices connect to the sim­u­lat­or, they trans­mit identi­fy­ing informa­tion. Po­lice can single out a device and use the direc­tion and strength of the sig­nal to ac­quire its location.

The Justice De­part­ment has his­tor­ic­ally re­mained highly se­cret­ive about the tech­no­logy, of­ten push­ing state and loc­al po­lice to stay si­lent about their us­age of the sim­u­lat­ors.

Stin­grays do not re­ceive GPS in­form­a­tion, and may not be used to in­ter­cept commu­nic­a­tion to and from mo­bile devices, or the data stored on them, according to the Justice De­part­ment.