What to do with your old Android phone before selling it

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Windows Phone
Josh Miller/CNET
Windows Phone only offers encryption for business customers. The easiest way to wipe a Windows Phone 7, 8 or 8.1, or Windows 10 Mobiledevice is to perform a factory reset and then load dummy data to overwrite traces of the original data.
Step 1: Open up Settings > About > Reset Your Phone.
Step 2: Confirm the action and then wait for the phone to wipe.
Step 3: Connect the phone to a PC and open My Computer. If you are connecting via Mac, download the Windows Phone app. Find the phone, which should show up as a removable device, and open it.
Step 4: Load dummy data onto the phone by dragging and dropping from another folder. Don't use your personal photos or documents here; instead choose files that contain no identifiable metadata that could be traced back to you, such as video or music files. Try and fill the phone with as much dummy data as possible.
Step 5: Reset the phone again using the same method as in step 1. Repeat the dummy data load a few more times to ensure all your original data is overwritten.
Step 6: Perform a final reset.
Log in to your Microsoft account at account.microsoft.com/devices and find the phone you just wiped. Remove it from your account.