Premium · v1 · July 2026

Lock a Chat.Lock the App.

Some conversations are nobody else's business. Lock one and its messages are encrypted with a key derived from your passcode, so the chat is unreadable without it. Locked chats still appear in the sidebar by name with a lock badge; open one with the passcode, with Touch ID on macOS, or with Windows Hello on Windows. A separate app lock holds the whole window at launch until you prove you are there. Both are optional, both are local, and neither sends anything to a server.

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Lock One Chat, Not Everything

Open a chat's menu and pick "Lock session". Set a 4-digit PIN and Plexon generates a random key for that chat, encrypts the conversation with it, and wraps the key under your passcode. The messages move out of the session file into a sealed record. Nothing stored on disk reveals the passcode, and every other chat carries on untouched.

  • "Lock session" sits in the same session menu as Rename and Share
  • Each locked chat gets its own key, so one passcode never opens another chat
  • A 4-digit PIN, stretched with argon2id before it becomes a key
  • AES-256-GCM seals the conversation and rejects a wrong passcode on the authentication tag
  • "Lock now" re-seals an open chat without closing the app

Touch ID and Windows Hello

Typing a passcode every time gets old. Turn on biometric unlock and the operating system holds a second key, in the Keychain on macOS or DPAPI on Windows, and releases it only after a fingerprint or face check. The passcode field never goes away. A biometric prompt can be cancelled, can fail to match, or can stop working after an OS update, and a lock with one way in is a lock that strands you.

  • Touch ID on macOS, Windows Hello face or fingerprint on Windows
  • The OS-held secret opens the same chat key your passcode does, so either works
  • Turn biometrics off later and the passcode still opens the chat

What a Locked Chat Will Not Do

A locked chat is inert until you open it. It stays in the sidebar with its name, its message count, and a lock badge, and that is all anyone sees. Export refuses instead of writing an empty file. Live Share has nothing to mirror. A Telegram message, a Slack message, or a scheduled job aimed at it comes back asking you to unlock it in Plexon first.

  • Export and .plexshare are refused with a clear message, never a silent empty file
  • The chat view, exports, and Live Share all read the same sealed content and get nothing
  • A background trigger stops at the lock rather than starting a turn it could not save
  • Renaming a locked chat still works: the lock covers the messages, not the name

The App Lock Is a Gate, Not Disk Encryption

Turn the app lock on and Plexon asks for a passcode, Touch ID, or Windows Hello before the window becomes usable. It stops the person who walks up to your unlocked laptop. It is not disk encryption. Your real protection for data at rest is FileVault or BitLocker, and Plexon makes no claim about a machine whose operating system is already compromised.

  • Stores a verifier, not your passcode, and re-encrypts nothing
  • Wrong attempts back off on disk, so relaunching the app does not reset the wait
  • When the gate engages it re-locks every session left open, so clearing it hands nobody an open chat
  • Lives in Settings under Security, next to the session lock defaults

Lock Again After Idle Time

The gate does not have to wait for the next launch. Pick how long Plexon can sit with no typing and no clicking, and after that the window locks itself, the way an OS screen lock does. "Only at launch" stays the default. You can also lock it yourself at any moment, and Plexon locks when your computer does. Locking covers the screen, it does not stop the work: a chat that is mid-answer keeps going behind the lock, and when you clear it everything is where you left it.

  • "Only at launch" is the default, or anywhere from 1 minute to 3 hours 30 minutes
  • Lock on demand with Ctrl+Shift+L, the tray menu, or the button in Settings
  • Locks itself when your computer locks or goes to sleep
  • Idle means nobody is at the keyboard, not that nothing is happening
  • A chat mid-answer keeps its key and finishes while the screen is locked
  • A laptop closed for an hour comes back locked: the check reads the clock, not a timer that slept through it
  • Sits with the app lock switch in Settings, under Security

One PIN Opens Both Locks

Clear the app lock with your PIN and any chat locked with that same PIN opens with it. You type it once at the gate instead of once more per chat. A chat on a different PIN stays sealed, because the PIN you typed does not unwrap its key. Touch ID and Windows Hello are the exception: the operating system hands back a check, not a PIN, and a check has nothing to try against a chat key.

  • One PIN at the gate opens the app and every chat set to that same PIN
  • A chat with its own PIN stays locked. Nothing about it is unwrapped
  • Touch ID and Windows Hello open the app only, never the chats
  • "Use my app PIN" appears when you set a session lock, making the two the same on purpose
  • The two are copies, not a link: changing one later leaves the other as it was

A Hard Stop on Guessing

A 4-digit PIN is 10,000 combinations. The backoff makes each guess slow; it does not put a ceiling on how many there can be. Set a limit on wrong PINs and there is one: reach it and Plexon deletes everything it keeps on this machine, the global folder and every project folder, then restarts as a fresh install. Off by default, and the lowest limit you can set is 5, so a mistyped PIN cannot trigger it. Wrong PINs at the gate and at every locked chat count toward the same total, and any correct PIN or biometric check puts the count back to zero.

  • Off by default. Enter 0 to keep it off; the lowest real limit is 5
  • The gate and every locked chat share one count, so moving between them buys no extra tries
  • A correct PIN, Touch ID, or Windows Hello clears the count
  • Closing the app part-way through does not cancel it: the erase finishes on the next launch
  • Deletes the global folder and every project folder Plexon knows about. Nothing is recoverable
  • Sits with the other lock settings in Settings, under Security

Premium to Turn On, Any Plan to Open

Setting a session lock, enabling biometric unlock, and turning on the app lock need the Premium plan. Everything else is ungated on purpose. Unlocking, re-locking, changing a passcode, and removing a lock work whatever your plan says, so a subscription that lapses never locks you out of your own chats.

  • Premium: set a session lock, enable Touch ID or Windows Hello, turn on the app lock
  • Any plan: unlock, re-lock, change a passcode, remove a lock
  • A downgrade leaves every locked chat openable with the passcode you already set

What the Locks Cover

Encrypted, Not Hidden

The messages in a locked chat are sealed with AES-256-GCM under a key only your passcode opens. Hiding a chat from view would be a display trick. This is not that.

Passcode or Biometric

Touch ID on macOS, Windows Hello on Windows. The OS holds the second key and releases it after a check, and the passcode keeps working either way.

A Gate on Launch

The optional app lock holds the window until you prove you are the one sitting there. It is a gate against the person at your desk, not a substitute for FileVault or BitLocker.

Local, and Not Recoverable

No passcode, salt, or key leaves your machine, and none of it reaches a Plexon server. That also means nobody can reset a forgotten session passcode, us included.