About Attention Aware features on your iPhone X or later

Even if you don’t enroll in Face ID, the TrueDepth camera on iPhone X or later intelligently activates to support attention aware features. For example, 

• When you’re looking at your phone, your display will not dim until you stop looking at your device.
• If you're looking at your device, it will lower the volume sound of your alerts.

If you don’t want to use these features, go to Settings > Face ID & Passcode and turn off Attention Aware Features.

• Use Face ID to securely unlock your iPhone, authenticate purchases, sign in to apps, and more—with just a glance.
• Use notifications on your iPhone, iPad, or iPod touch.