iOS 12 allow you to add second person to your iPhone’s Face ID recognition as alternate appearance. Follow these steps to add alternate appearance on iPhone.
Step 1: Open Settings app.
Step 2: Scroll down and select Face ID & Passcode.
Step 3: Enter your passcode.
Step 4: Tap on Set Up an Alternate Appearance.
Step 5: Tap on Get Started at the bottom.
Step 6: Go through the Face ID scan process.
Step 7: Tap Done at the bottom once complete.