While many studies, such as the one recently conducted by antivirus vendor Kaspersky, show that the majority of secondhand electronic devices still contain personal data from their previous owners, it is easy to dispose of them, making sure not to leave any trace behind. Here’s an example of how to do it with one’s smartphone.
In order to prevent your personal data from circulating ― whether it be private photos, administrative documents or credit card numbers ― without your knowledge, it’s important to respect principles of common sense. And so when you change device, before parting with your old smartphone, you should back up all of your multimedia data (audio, photo, video and various documents), either by copying it to your computer or by taking advantage of online storage services such as Google Drive and Google Photo.
Once all these operations have been performed, it is then time to reset your phone, by going to Settings / System and Updates under Android or General / Reset under iOS. When specified, make sure to erase all data, ie., restore the original factory configuration. You can then give it away, resell it or put it away permanently at the bottom of a drawer with total peace of mind