The NSA has a reputation for spying on whoever they please and mass data collection from people who aren't suspects in crimes, and the agency can listen in on your conversations through your iPhone's built-in microphone even if the device is turned off. That trick can't, however, happen unless the NSA has gained physical access to your iPhone and installed either a hardware or software implant designed to make it appear your smartphone is off even though it isn't.
Think your smartphone is safe when it's off? The NSA may still be able to activate it's mic.
The idea that the NSA, or National Security Agency, can remotely activate your iPhone's microphone and listen in on your conversations surfaced when Edward Snowden leaked secret government documents a year ago documenting widespread surveillance on U.S. citizens as well as citizens from other countries.
To use your iPhone's mic as a clandestine eavesdropping tool, NSA agents must first get their hands on your smartphone and install hardware or malware that makes it appear as if your iPhone has completed a normal power down sequence, but leaves the device on so they can remotely trigger the mic, according to Wired.
Once in place, the NSA implant can present users with a fake "slide to power off" display, or interrupt the shutdown sequence so the device seems to fully shut down, but instead is simply unresponsive. With the iPhone on -- or seemingly off -- NSA agents can listen in on your conversations even if you aren't talking on your phone.
Considering the process requires hands-on modifications to your iPhone, it isn't likely the NSA is listening through our mics en masse. That said, there's little to stop the NSA from finding iPhone shipments before delivery and installing their hacks before you ever see your brand new smartphone. As far fetched as that sounds, reports claiming the agency has done just that with Cisco's wireless routers.
If you're concerned that the NSA is listening in on your conversations, the easiest fix is to make sure your smartphone, whether it's an iPhone or other model, isn't near by. Mr. Snowden put his smartphone in a refrigerator to block signals, and apparently putting and iPhone into what's called DFU mode.
DFU mode is a reset mode that disables all of the iPhone's radio transmitters and receivers, and leaves only the Dock connector or Lightning port active. The feature is there so technicians have an easy way to completely reset iPhone firmware when the device isn't working properly. It's a drastic move, but will keep your iPhone from functioning at all while in that state.
To place your iPhone into DFU mode, press and hold the power button for three seconds. Continue to press the power button and hold down the Home button for ten seconds. Release the power button, and continue to press the Home button for ten more seconds. At that point, your iPhone will wait for a physical connection to a computer before returning to a normal functioning state.
Assuming the nature of your conversation is so sensitive that you're concerned about NSA eavesdropping, you're better off making sure there aren't any smartphones, computers, or tablet devices anywhere near by. Maybe consider driving deep into the wilderness and then hike away from your car, too. Tin foil hats are optional.