In my Scientific American column this month, I wrote about how the police were able to recover my stolen iPhone. How? By going to the house identified by the free Find My iPhone service, a satellite picture of which I had sent to my Twitter followers.
Such public location announcements get into murky privacy territory. But at the end of the day, when your phone is lost, Find My iPhone—and similar services for other phones—can be fantastically useful. Sometimes a bad guy has made off with your phone. Sometimes you've just left it somewhere in the house. In either case, it's nice to be able to track it (whether or not you decide to post the results to the Internet at large). Here's how you go about setting this up for your own iPhone or Android phone.
iPhone: Sign up for a free iCloud account, if you don't have one, at www.icloud.com. Then, on the iPhone or iPad, tap Settings, tap iCloud and turn on Find My iPhone. Confirm your decision, and maybe take this opportunity to password-protect the phone, just in case.
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When the day comes that you and your phone have parted, visit icloud.com on any computer or other phone. Log into icloud.com. When you click Find My iPhone, you're shown your phone's location on a map.
You can also make your phone start pinging loudly (in case it's under a couch cushion in your house) or send a message to its screen (in case whoever found your phone genuinely wants to contact you).
You can even click Lock to password-protect the thing remotely or Remote Wipe, which erases the phone's data, wherever in the world it is now. That last-ditch option is great if you consider your photos, documents and e-mail private.
Keep in mind that all of this works only if the phone is on. If it's in Airplane Mode, out of battery power or just off, Find My iPhone can't find your iPhone. And it works only if it hasn't yet occurred to a thief to connect the phone to a computer running iTunes and erase it that way, a step that makes the phone totally unfindable.
Android phone: Go to the Android app store (Google Play) and download a phone-finding app. I like Where's My Droid (wheresmydroid.com, free), which works on any recent Android phone.
If your phone goes missing, you can send, via text message, a special password to activate the app. That makes the phone ring at maximum volume for 30 seconds. A different code sends you a link to the phone's location on a map. If you buy the Pro version for $4, you also get a Remote Wipe feature.
And what if you didn't think to install an app before you lost the phone? In that case, you can remotely download an app called Plan B. When you do that, the app auto-opens and sends the phone's location to your G-mail address.
Finally, some apps can actually take a secret photo of whoever's using the phone and e-mail it to you, which can sometimes provide an essential clue or bit of proof. For Android, a feature called Candid Camera performs this task—it's part of the free TrustGo Mobile app. You can get that feature on the iPhone only if you "jailbreak" it—hack your way past Apple's app-installation system—and install an app like IGotYa or ICaughtU.