Locking one chat is different from locking the app.
App lock, the subject of our WhatsApp privacy settings guide, asks for a fingerprint before the whole app opens. Chat lock does something narrower and often more useful, it hides one specific conversation behind its own fingerprint check while every other chat opens normally, so a phone can be handed to someone else for an ordinary reason without a single thread needing to be explained.
The distinction matters because most people do not want every conversation behind a second lock, only the one that would otherwise sit at the top of a chat list with a booking's details visible in the preview line. A phone handed to a colleague to show a photo, or to a child for a game, opens normally in every other respect.
Setting it up on WhatsApp.
Open the conversation, tap the contact name, and look for Lock This Chat. Confirming it moves the conversation out of the main list entirely and into a separate Locked Chats folder, which itself sits behind the same fingerprint or face check used for app lock. The chat's preview, its unread count and its typing indicator all disappear from the ordinary list at the same moment.
Unlocking it later is a fingerprint check on the folder itself, after which the conversation opens exactly as it always did. Locking a chat changes where it lives, not how it behaves once you are inside it, so messages send, arrive and display normally the entire time.
If your version of WhatsApp does not offer it yet.
Chat lock reached WhatsApp later than most of the app's other privacy features, so an older, unupdated copy of the app may not show the option at all. Updating through your phone's own app store usually resolves this within a few minutes, and it is worth checking the app's version number under Settings, Help, App Info if the Lock This Chat option seems to be missing. Older phones running an outdated operating system occasionally cannot install the newest app version at all, worth knowing before assuming the setting has simply been misplaced.
Until an update is possible, archiving the conversation combined with app lock covers similar ground, moving the chat out of the main list while still requiring a fingerprint to open the app that contains it, a reasonable stand in rather than a full substitute.
What a locked chat looks like from the outside.
To anyone else scrolling the main chat list, a locked conversation is simply absent, not present with a padlock icon inviting curiosity. The Locked Chats folder itself is a single row near the top of the list, unremarkable next to any other folder a phone might have, and it asks for the same fingerprint whether one chat is inside it or several. It reads, at a glance, like any other organisational folder a busy chat list might reasonably have.
This is the detail that makes chat lock worth the thirty seconds it takes to set up. A hidden folder that announces itself as hidden defeats much of its own purpose, and WhatsApp's version is deliberately plain, closer to an ordinary folder than to a vault with a sign on the door.
Notifications on a locked chat.
By default, a locked chat's notifications drop the sender's name and message preview, showing only that a message has arrived somewhere, nothing more specific than that. This closes the one gap chat lock would otherwise leave open, a lock screen notification printing exactly the line you moved the conversation to avoid.
The setting sits alongside the lock itself and is worth checking once, since notification behaviour occasionally changes with app updates and is easy to overlook after the initial setup. Send yourself a test message from another number after locking a chat and glance at the lock screen, the quickest way to confirm the preview genuinely stayed hidden.
The same idea beyond WhatsApp.
Telegram offers a comparable result through its secret chats, detailed in our separate guide, though the mechanism differs, a secret chat is its own conversation rather than a lock applied to an existing one. Signal, covered in our guide to Signal, relies on the phone's own screen lock rather than a built in chat lock feature of its own, which is one more reason a good phone lock still matters whichever messaging app carries the actual conversation.
Deciding which chats earn it.
A single booking thread is the obvious candidate, and it takes the same thirty seconds whichever companion the conversation is with. It suits a girlfriend experience arranged from Oud-Zuid exactly as well as any other format, and companions filed under slim or brunette receive the message identically either way, since locking a chat changes what your phone shows, not what reaches us. The booking page explains what the conversation itself needs to contain.