Take these steps to secure your phone before letting anyone—even your friends—borrow it | Popular Science
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Take these steps to secure your phone before letting anyone—even your friends—borrow it

Keep your secrets safe.

Phone security

Don't lend out your phone without reading this guide.

When somebody asks to borrow your phone—perhaps a stranger asks to make a call, or a friend wants to scroll through your vacation photos—the thought can give you heart palpitations. We keep so much data and personal information on our little pocket computers that handing them over to others, even voluntarily, can seem like an invasion of privacy. But you don't have to feel that way. Both Android and iOS include built-in options for restricting what guests can do on your smartphone.

These security tips differ from the general lock-screen protections we've previously discussed. That advice—for example, you should always have a PIN code protecting your phone—keeps your information safe from anyone who might steal or accidentally encounter your device. But in this guide, we're looking at situations where you willingly hand over your smartphone.

Android

When the 5.0 Lollipop version of Android launched in 2014, the cellular operating system began including a feature called screen pinning. Essentially, this mode locks the phone's user inside one specific app, such as a game or a photo gallery. When a guest holds a screen-pinned phone, they cannot open other apps or change the settings unless they know the PIN that unlocks full access to the device.

To set up screen pinning, go to Settings and tap Security & location, then Screen pinning. Toggle the switch to On and make sure the option to always ask for a PIN before unpinning is set to On as well. Next, open up the app you want to let your guest access, then tap the Overview button (the square on the right side of the navigation bar); recent apps will appear in a line, with the app you just accessed front and center. Drag that app to the middle of the screen, then tap the thumbtack-shaped pin button that shows up in the bottom right corner of the thumbnail. Congratulations—only that app will now be accessible to users. To restore your phone's full function, press the Back and Overview buttons at the same time and enter the PIN code for your phone.

If you want to take further precautions, or you have one friend or relative who's constantly borrowing your device, try out Android's guest mode. This ability, like screen pinning, first appeared with the advent of Lollipop. It gives a frequent phone borrower their own user account, complete with independent apps, browser settings, and more. Compare it to the way that one computer can host different users, where each user gets his or her own settings, files, and layout. When someone else is using your phone in guest mode, they cannot return to your account or access your files without your unlock code.

To find guest mode, drag down with two fingers from the top of the screen, then tap your user avatar and select Add guest (for new guests) or Guest (for those who have already used your device in this mode). If there's a specific person who borrows your phone a lot, you can give them their own named account by tapping Add user. Inside guest mode, users cannot send texts, make calls, or access the usual backup and reset features. However, the guest can sign into apps using his or her own accounts, and if they have Google credentials, they can then access apps like Gmail and the Google Play Store. When your friend hands your device back to you, you'll want to return to your own account: Again drag down from the top of the screen with two fingers, then tap the guest avatar and choose your own user account again. While your guests could try to switch users without your knowledge, they would have to get through the lock-screen protection on your account—so effectively, you're the only one who can get back to your own apps, files, and settings.

If those two options still aren't enough for your needs, download AppLock Fingerprint Unlock, a free Android app that lets you protect any app on your phone with a fingerprint test. For example, if you want to lend someone your phone, but keep them out of Snapchat and Facebook, then AppLock can help.

iOS

On one of Apple's smartphones, the Guided Access feature can help protect your iPhone from whoever's borrowing it. This mode restricts guests to just one app of your choice, which means they won't be able to escape into any other app, or change your settings, without the correct PIN code or Touch ID authorization.

To set up Guided Access, open Settings and then select General, Accessibility, and Guided Access. The subsequent screen lets you turn the feature On or Off, and set whether you want to use a PIN code or Touch ID to unlock the mode. If you're going to put a limit on the Guided Access restriction, you can also configure the alarms here. Open up the app you want to restrict your guest to, triple-tap the Home button, and the Guided Access menu appears. From this initial screen, you can disable certain areas of the display, such as the menu button, for example. You can also tap Options to set time limits and disable or enable certain functions, such as the Sleep/Wake button and touch input. Right before you hand your phone over to a friend, tap Start to enter Guided Access mode and apply the restrictions you've put in place. Another triple-tap on the Home button, along with the correct PIN code or fingerprint, will disable Guided Access once more.

Unlike Android, iOS doesn't offer multiple user accounts or third-party locking apps. However, if Guided Access doesn't quite work for you, you do get a couple other options that are worth mentioning.

The first is a long list of parental controls, which you can find in Settings under General and Restrictions. These options control users' access to the web, camera, certain types of age-sensitive content, and so on. Admittedly, you won't want to run through all of these every time you pass your phone to a friend. But if you regularly hand over your iOS device to a young family member, it might be worth your while to set them up. To lock and unlock these device restrictions, you'll need a PIN code.

Finally, if you're specifically interested in keeping certain photos and videos private—and you aren't too concerned about anything else on your phone—you can hide images and clips from the iOS Photos app. Simply tap the Share button and then choose Hide. This hides the chosen photos and videos from the Moments, Years, and Collections views, although a determined seeker can still access them through a search or via the Albums screen.

Whether you're lending your phone to a stranger, friend, or family member, some combination of these tips should cover every Android or iOS eventuality. But if you really don't trust someone with your property, your path is much more straightforward: Don't hand them your phone in the first place.

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