Apple has at long last made an iOS app for Find My iPhone, enabling the discovery of the location of MobileMe-registered iDevices of all types from within an app. At the same time, Apple has modified me.com in several ways, including improvements to the Find My iPhone Web app, which now matches the new iOS app in form and function. Both the iOS app and Web app make it far easier to choose a device and locate it quickly.

How Find My iPhone Works -- Find My iPhone uses the location services built into mobile Apple devices in conjunction with the Push and automatic Fetch options for information retrieval from MobileMe.

How a device reports its location to MobileMe depends on its built-in radios and receivers. An original iPhone determines its location by scanning for Wi-Fi and cell towers, and it reports its location over either Wi-Fi or cell data connections. An iPad with Wi-Fi only or an iPod touch can scan for Wi-Fi networks, and it needs an active Wi-Fi network connection to upload information.

The iPhone 3G and 3GS, the 3G iPad, and the upcoming iPhone 4 all use Wi-Fi and cell tower triangulation combined with an internal GPS receiver. Each device reports its location over Wi-Fi, EDGE, or 3G connections. (A 3G iPad that doesn't have an active cellular data plan can still look up its location using its GPS and cell tower locations if the cell radio is turned on, but it requires an active Wi-Fi link to report its whereabouts.)

Find My iPhone requires an individual or family pack MobileMe account; an email-only account won't work.

To enable Find My iPhone/iPad/iPod touch on a given device, tap Settings > Mail, Contacts, Calendars, and tap your MobileMe account under Accounts. Set the Find My iPhone switch to On, if it isn't already, and tap Done.

In the Settings > Mail, Contacts, Calendars > Fetch New Data view, either or both Push and Fetch need to be active. If Push is set to Off and Fetch is set to Manually instead of a recurring interval, Find My iPhone cannot work, because the location is never updated. Apple recommends Push for MobileMe.

The New Find My iPhone App -- Before the Find My iPhone app, you had to log in to me.com from a computer's Web browser, click a Find My iPhone link, and re-enter your password (for additional security, since an initial login can remain active for up to two weeks), and then MobileMe would ping the devices registered to your account to get the current location. (Eventually, it became possible, though fussy, to use the MobileMe Web site from Mobile Safari; see "MobileMe Web Site Adds Some Mobile Safari Support," 18 February 2010.)

The Find My iPhone app makes this a simpler task. Launch the app, and you're prompted for a MobileMe account and password. You can't store the password, and the app logs out automatically after 15 minutes for security's sake. (Imagine someone stealing your iPhone or iPad and using a stored password in this app to find your other iDevices!) You can't view multiple accounts' iDevices at once, as might be useful in a family situation or where multiple devices were stolen (see how Adam and Tonya use the service in "Find My (Wife's) iPhone," 23 September 2009).

The main screen of the app on an iPhone or iPod touch shows a list of devices with Find My iDevice enabled and registered to the account you used.

On the iPad, the main view shows the location of the first item in the alphabetical list of devices by default. To see a full list of registered devices, tap the Devices button at upper left. The Devices popover lists each device and whether it is currently being located or how long ago the location was established. A Refresh button on the toolbar lets you try to grab a newer location.

To see a device's last known location in the main view, you tap its name in the popover. The last known location is displayed on a map using Google data, in which you can switch among map, satellite, and hybrid views.

To interact with the device remotely, on an iPhone or iPod touch, tap the detail button beside a device's name; on an iPad tap the info button (an "i" in a circle). The resulting screen on all devices lets you choose among the three behaviors you can inflict on the remote device: Display Message or Play Sound, Remote Lock, and Remote Wipe.

Just as with the Web app for Find My iPhone, you can send a message to the device and/or (not just "or" as the label suggests) play a sound that can't be muted and that will play regardless of audio settings or the mute switch's position.

You can also remotely lock a lost or stolen device with a four-digit PIN, which immediately locks the device; or wipe the device's storage. On an iPhone 3GS, upcoming iPhone 4, or any iPad, the wipe happens in seconds, due to hardware encryption; on any other device, the wipe can take minutes to hours, depending on how much you've stored on it.

Improved Web App -- The previous Web app version of Find My iPhone was starting to look a bit like the dog's lunch if you had registered multiple devices with a single MobileMe account: a long scrolling window with maps interspersed with buttons and explanatory text. The revised version looks and works nearly the same as the Find My iPhone app. A Devices list at left shows registered mobile gear.

The first item in the list is shown on a map. You can click any device in the list to have it show its current or last known location, if any.

Click the detail button for the device, and the three behavior options appear. Click any of the buttons, and further options appear, such as sending a message to the device and playing a sound.

As with the Find My iPhone app and other iOS software like Maps, a device with an active GPS that's locked onto satellite coordinates is shown as a single blue dot. A device without a GPS or that hasn't locked on is shown as a blue dot centered within a shaded blue circle that represents the margin of error.

Better and Faster Than Before -- Being able to walk around with the Find My iPhone app may make it easier to find a lost device or work with the police to recover a stolen one. Plus, the Web app's update improves how quickly and easily you can find a device's location from any computer.