Since the iPhone X was announced, much of the discussion has been focused on Face ID, Apple’s new biometric replacement for Touch ID. How does it work? Is it safe? In a new interview with Craig Federighi, Apple’s SVP of Software Engineering, TechCrunch learned the secrets behind what makes the technology tick.

The interview is wide-ranging, from how Face ID was developed to the security and privacy behind the technology. Federighi provides great insight into the new feature, which he personally had an embarrassing experience with while attempting to demonstrate it onstage during the iPhone X’s announcement.

According to Federighi, Apple gathered a billion images to analyze for Face ID, and then later got consent from subjects to provide scans that he said were “quite exhaustive.” The scans that were needed to thoroughly train Face ID were taken from many angles to ensure the highest possible quality.

Federighi said Apple will never share Face ID information with anyone, including law enforcement. That’s because Apple doesn’t have access to what’s scanned by Apple’s Face ID system. All data is stored in the iPhone X’s Secure Enclave, which is the same method Apple used with Touch ID.

Federighi also said Face ID can quickly be disabled by users by pressing and holding the iPhone X’s side buttons.

“So, if you were in a case where the thief was asking to hand over your phone—you can just reach into your pocket, squeeze it, and it will disable Face ID,” Federighi said.

Finally, Federighi said while Face ID works incredibly well in all lighting conditions, the system has a difficult time recognizing people when they’re wearing certain sunglasses.

“It turns out that polarization isn’t the issue—I have a set of polarized sunglasses that work just fine with Face ID,” Federighi said. “What it is is that different lenses have a different amount of infrared filtration. Most let enough IR through that through most lenses your eyes are visible to IR even if they’re not visible to the human eye.”

TechCrunch’s interview with Federighi is full of insight into Face ID, so check out the link below to learn more. Consumers around the world will get a chance to try Face ID when the iPhone X officially launches on November 3.