With iOS 7 or later, Find My iPhone includes a feature called Activation Lock, which is turned on automatically when you set up Find My iPhone. Activation Lock makes it harder for anyone to use or sell your iPhone, iPad, or iPod touch if it’s ever lost or stolen.
With Activation Lock, your Apple ID and password are required before anyone can:
==> Turn off Find My iPhone on your device
==> Sign out of iCloud on your device
==> Erase and reactivate your device
If you want to give away or sell your device, be sure to erase your content and settings (in Settings > General > Reset > Erase All Content and Settings). When you erase your content, Find My iPhone and Activation Lock are also turned off.
You can check the Activation Lock status of your iPhone or iPad at icloud.com/activationlock from a Mac or PC.
It’s highly recommended you check the status if you’re purchasing or selling a used device.