You are, we hope, already protecting your phone with a PIN, a fingerprint, or a face (or all three), but sometimes you’ll want to add an extra barrier to particular apps—if you’re lending your phone to a friend, say, or if your kids or partner are always borrowing your phone for whatever reason.

How you want to apply this additional protection is up to you. Some apps come with it built in; in other cases you’ll need to enlist the help of a third-party app. The process is also different depending on whether you’re using Android or iOS, and so we’ve split our guide up into two sections.

Locking Apps on iOS

Apple doesn’t give third-party apps quite as much leeway on iOS as Google does on Android, so you won’t find any general-purpose locking tools in the App Store. Instead, you’re relying on the individual apps themselves—many apps that can hold sensitive information will give you additional options.

Apple’s own Notes app for the iPhone is one example. You can lock individual notes by tapping the Share button (inside a note) or long-pressing on a note (on the notes list) and then choosing Lock Note. Notes are locked using Face ID, Touch ID, or a PIN code, and you can set this via Notes in the iOS Settings app.

WhatsApp has protections in place as well to keep prying eyes out of your messages. From the main screen, you need to tap Settings, Account, Privacy, and Screen Lock—you’ll then be able to set up Touch ID or Face ID to guard access to your conversations. If either of those methods fail, you’ll get pushed back to your phone’s lock screen passcode.

Another third-party app with this same security measure is Dropbox, which is handy if you don’t want your toddler accidentally wiping all your files with an ill-judged finger push. Tap Account, then the cog icon (top left), then Turn Passcode On. When you’ve set a passcode, you’ll also be given the option to use Touch ID or Face ID as well.

We can’t guide you through every app on iOS, but have a look inside your favorite ones to see if an extra security layer has been included. Evernote, Amazon, and PayPal are three other apps that can be locked with Touch ID or Face ID, and many banking apps now have the same feature too, so even if someone gets access to your phone (with or without your permission), they can’t access all of your apps.