Lock Carlo with Face ID

Open the More menu from the tray, tap Settings, then Security, and turn on App lock. Carlo confirms it is you once, and the lock is on. From then on it asks you to unlock when you open Carlo fresh and when you come back after leaving it.

Tap Require unlock to set how soon that happens: Immediately, After 1 minute, or After 5 minutes. The middle ground exists because you do not always want to re-authenticate after glancing at a text, so the one and five minute options let you pop back in without unlocking if you return quickly. Opening Carlo fresh always asks, whichever you choose.

While the lock is on, Carlo also hides its screen in the app switcher, so a glance at your open apps never shows your finances. On Android it blocks screenshots and screen recording too.

App lock leans on your phone's own lock, so if your phone has no Face ID, fingerprint or passcode set up, Carlo cannot turn it on and will ask you to add one first. Carlo never stores any of those: your phone answers the challenge and Carlo only hears yes or no.

To switch it off, return to Settings → Security and turn App lock off. It stops asking right away.

What this is and is not: it is a privacy lock over the screen, not a second layer of encryption. Your data is already encrypted whether or not app lock is on. What it adds is stopping someone holding your unlocked phone from opening Carlo. It is also per-device, so turning it on here does not turn it on across your other phones.