They can at least track location while the phone is 'powered off'. https://www.techdirt.com/articles/20130723/12395923907/even-powering-down-cell-phone-cant-kee

They can at least track location while the phone is 'powered off'. https://www.techdirt.com/articles/20130723/12395923907/even-powering-down-cell-phone-cant-keep-nsa-tracking-its-location.shtml https://www.techdirt.com/articles/20130723/12395923907/even-... "According to Ryan Gallagher at Slate, the NSA, along with other agencies, are able to something most would feel to be improbable, if not impossible: track the location of cell phones even if they're turned off. On Monday, the Washington Post published a story focusing on how massively the NSA has grown since the 9/11 attacks. Buried within it, there was a small but striking detail: By September 2004, the NSA had developed a technique that was dubbed “The Find” by special operations officers. The technique, the Post reports, was used in Iraq and “enabled the agency to find cellphones even when they were turned off.” This helped identify “thousands of new targets, including members of a burgeoning al-Qaeda-sponsored insurgency in Iraq,” according to members of the special operations unit interviewed by the Post." And possibly capture data... "The FBI's use, in which cell phones' microphones were remotely activated to record conversations (even with the phones turned off), probably had some bearing on Snowden's request that journalists power down their phones and place them in the fridge. "