How to completely delete data from the phone before selling?

If you didn't know, when you reset your phone to factory settings and think that all the data was destroyed that way, you're wrong!

Restoring the phone to factory settings works like classic deleting files, which means that the files are still in the phone but the information about their existence is deleted so that other content can pass over them. Only when some other content is written over old data, do they disappear forever. I've already written about this, so take a look:

Are you selling a phone? A factory reset is not enough!

Now, if you want your files to be inaccessible to the next phone owner, you need to go one step further in the process of deleting data. And that step is called encryption.

How to completely remove personal data before selling the phone?

1. Back up ALL data because you will not be able to restore it after this process
2. Encrypt your phone by entering the phone settings, then "Security", then "Encrypt device", and finally "Set screen lock type". This way you will choose a password that you will have to enter every time you start your phone and all the data is encrypted.
   
   
   
   Note: the encryption process can take a long time, so expect at least an hour! Also, charge the battery to 80% and put it on the charger if necessary.
   
   
3. You can now reset to factory settings by entering the settings, then to "Backup and reset", then "Factory data reset" (Factory data reset), and finally "Reset phone" (reset phone).
4. Wait a minute for the phone to return to factory defaults and you're done! This takes a few minutes and you never remove the battery during this process.

Now if someone tries to recover files, they will only see a bunch of strange symbols, signs, and numbers, that is your data mixed with a special algorithm. The only way to read this data is with your key.

An alternative

Another way to permanently remove certain files from your phone is with Avast! Anti-Theft applications. This application has a tool that deletes (thorough wipe) files forever, and can not be restored. So it not only deletes the information about the existence of the file but really removes the file from memory. But the process takes longer than the classic deletion.