By default, Apple’s iPhones and iPads make a sound when you turn their displays off (aka when you “lock” them). You can disable this sound entirely and never hear it again, or just silence your phone if you’d rather not hear it in certain situations.
How to Permanently Disable the Lock Sound
You can disable this sound from the Settings app. To do so, open the Settings app, scroll down, and tap the “Sounds & Haptics” option. On iPads and older iPhones, tap the “Sounds” option instead.
Scroll down to the bottom of the screen and locate the “Lock Sound” option. Tap the switch to the right of it to toggle lock sounds off. When the switch is in its leftmost position—that is, when it appears white and not green—the lock sound is off.
How to Temporarily Silence the Lock Sound
If you like the lock sound but just want to silence it in certain situations, you can just flip the physical Ring/Silent switch at the top left corner of your iPhone. The iPhone will be placed in silent mode, and the word “Silent” will appear on the screen for a moment.
This also silences other sounds, including the phone’s ringer (it will vibrate instead), keyboard clicks, and sounds played by apps. Flip the switch once again to take the phone out of silent mode.
Newer iPads don’t have a physical switch you can flip to enable silent mode. Instead, on an iPad, you must swipe up from the bottom of the screen and tap the bell-shaped icon. The words “Silent Mode: On” will appear and the icon will turn red. Tap it again to disable silent mode.
Even after you disable the lock sound, your iPhone will still lock when the screen turns off. You’ll need a passcode, Touch ID, or Face ID to unlock and use it.