Encrypt Your Data
You don’t need fancy software to securely wipe your phone and make it ready to sell or donate. You need to encrypt it first. This is the only step; it is a bit more time-consuming than simply resetting your phone. It ensures that someone with the skills to get to the data. You left behind will have to tear down one heck of a wall to do it. Bear in mind that the process can’t be reversed.
Head to the Settings app, and under Security, you’ll see a few settings for device encryption. If you’ve got an expansion slot, your device might also offer you the option to encrypt the inside SD card. Still, you don’t need to worry about that if you pop it out and keep it for yourself.
The device will take a while to encrypt, depending on how much data you have. Often up to an hour. But when you’re all done, you can perform that factory reset. Knowing that your information is technically still in all the blank areas of your phone’s storage. It’s encrypted and can’t be easily read.