Using Find My iPhone can significantly increase the odds that your lost iPhone will be returned to you. But it won’t work if the battery is dead.
With iOS 8, you now have the ability to have your missing iPhone send its location to Apple just before the battery dies.
This is probably most useful when looking for a lost iPhone. A stolen phone is more likely to be moved after the battery dies. Go to Settings > iCloud > Find My iPhone and toggle Send Last Location on (turn Find My iPhone on too if it’s not already enabled). This will cause your iPhone to send location data to Apple whenever the battery gets critically low. (This will not work if Airplane mode is on since a cellular or Wi-Fi connection is required to send the data.)
To find your missing dead iPhone, log in to iCloud on a computer and open Find My iPhone, or open the Find My iPhone app on an iDevice. Click on the missing iPhone and you will be shown the location where the phone was when the battery died. If you are using the app, you can click on the car icon for driving directions—although if you are the one who lost the phone, you presumably already know how to get back to the place where you left it.
This is from iPhone Life’s Tip of the Day series [Link]