When you’re not using iPhone, press the Sleep/Wake button to lock iPhone. Locking iPhone puts the display to sleep, saves the battery, and prevents anything from happening if you touch the screen. You can still get phone calls, FaceTime calls, text messages, alarms, and notifications. You can also listen to music and adjust the volume.
iPhone locks automatically if you don’t touch the screen for a minute or so. To adjust the timing, go to Settings > General > Auto-Lock.
Turn iPhone on. Press and hold the Sleep/Wake button until the Apple logo appears.
Unlock iPhone. Press either the Sleep/Wake or Home button, then drag the slider.
Turn iPhone off. Press and hold the Sleep/Wake button until the slider appears, then drag the slider.
For additional security, you can require a passcode to unlock iPhone. Go to Settings > Touch ID & Passcode (iPhone 5s) or Settings > Passcode (other models). See Use a passcode with data protection.