Turn Attention Aware features on iPhone X
Even if you don’t enroll in Face ID, the TrueDepth camera on iPhone X intelligently activates to support attention aware features, like dimming your display if you aren’t looking at your device or lowering the volume of alerts if you're looking at your device.
If you don’t want to use these features, go to Settings > Face ID & Passcode and turn off Attention Aware Features.