We all like to share our technology, but phone borrowers have an annoying habit of looking at things they're not supposed to: opening dating profiles and private photos, noticing financial or work-sensitive data and generally drifting into forbidden areas. If only you could stop this!
In fact you can. Many apps allow you to set a password (or Touch ID) lock that's required before you can even open them, while others let you lock individual files and notes. In this tutorial we show how.
For more general advice on this topic, have a read of our iPhone security tips.
Which iPhone apps allow you to set a lock?
Apple has opened up Touch ID to third-party apps in general, but in our experience it's mostly banking apps that have taken the company up on the offer - they're the ones where inappropriate access could be most damaging. Some shopping and payment apps have followed suit, such as PayPal, as well as password managers such as 1Password.
How to set a lock on an iPhone app
In general, and if you're not sure whether an app supports this feature, open it, go to the Settings and look for any reference to a password or, more likely, Touch ID.
As a guide to how this generally works, here's how to set up Touch ID or password locks on a few apps where we've seen it implemented.
The Barclays app we used to manage our current account offers a Touch ID option on top of the passcode lock it includes by default. Once this is activated you'll be able to unlock the app with a fingerprint, but if you get it 'wrong' (use the wrong or an insufficiently clean finger, presumably) three times you'll have to enter the passcode instead.
If you've got an iPhone X, you can set up Face ID instead, and this allows you five attempts before pushing you back to the passcode.
To activate these locks, tap the More icon at the bottom right of the screen, then Settings. Under the section titled 'Log-in and security', tap Touch ID (or Face ID), then tap the slider on the subsequent page so it turns green. You'll need to re-enter your passcode at this point.
This personal finance app can be locked too.
Open the app and go to the Settings, then tap Passcode & Touch ID. Select and tap Use Passcode so its slider turns green, and enter a passcode when directed. Then you can go back and tap Use Touch ID to turn that on.
The above process is limited to apps that have chosen to implement the feature, but if you've got a jailbroken iPhone you can make any app password-protected.
Open Cydia, then search for and install the app Lockdown. When it's ready, open Lockdown, enter a password and confirm. Now you just need to select the app you wish to lock from the list, then tap Lock. You can repeat this for multiple apps.
Apple's own apps
By default, you can do quite a lot with a locked iPhone: you can still access Siri, for instance, and check the Notification and Control Centres. You may even be able to reply to messages.
If you'd like to lock down these functions more tightly, go into Settings > Touch ID & Passcode (you'll have to enter your passcode), scroll down to the 'Allow access when locked' section and start de-selecting green options so they turn white.
Apple's Notes app is a slightly unusual case. You can't lock it down completely, but you can set a password/Touch ID lock on any individual notes you consider sensitive.
Open the Settings app and go to Notes > Password. Here you'll be able to set up a password and activate 'Use Touch ID'.
With this setting enabled, open Notes and find the note you want to password-protect. Tap the share icon at the top righthand side of your screen and select Lock Note.
More related advice can be found in our roundup of Notes tips.
The most extreme way to lock your apps is to use Guided Access. This locks you into a single app and requires a password before letting you open anything else.
The first thing to do is to make sure Guided Access is activated and ready to go - once it is, you then switch it on fully by triple-pressing the Home button.
Open the Settings app and go to General > Accessibility. Scroll down almost to the bottom and check Guided Access. Does it say On? If not, tap to enter the section and turn it on. (Even if it's on already, it's probably worth going in anyway to check the settings.)
Now go into the app you wish to be 'locked in' and triple-press the Home button. You can now disable areas on the screen by circling them, or just tap Start at the top right if you want to allow full use. Set a passcode.
You'll now find that pressing the Home or power button doesn't work: the only way out is to triple-press the Home button again and enter the passcode you set earlier. Now you can tap End (or simply press the Home button again).
How to password-protect files and folders
If you just want to lock certain photos, say, rather than the entire app those photos are stored in, you've got other options.
Apple doesn't allow this function natively, but what you can do is download a dedicated, lockable app for this purpose and save the sensitive files to that. Anyone using the iPhone will need to enter the chosen password before accessing the files in the locked app.
Our colleagues at Tech Advisor suggest an app called Folder Lock, which is free (although a paid-for version adds extra features). After saving files to this app remember to delete the on-device originals in the other app, because Folder Lock doesn't do that for you. You should as ever keep off-device copies of important files as a backup.