Having recently migrated from my old phone to a new one due to technical issues faced in the former, I ended up with a deal to sell my old handset to a repair center guy the very next day for financial takeaway to get the new one. Subsequently, I followed a few steps to ensure all data from my phone was wiped out.

In contrast to my situation wherein I had both my old phone (for a day) and my newly obtained phone, here are steps I followed in order to ensure nothing related to me is remnant in my old phone after resale:

• Backing up data - In order to access the same content you had on your old phone, you’ll need to back up everything to the cloud (servers) or your local machine (PC which may be a desktop/laptop) in case data isn’t already backed up.
  For stuff like pictures, videos, music files, and documents, one can easily transfer them via USB to one’s local machine. But then you won’t be able to apply the same procedure for exceptions like WhatsApp, inclusive of chat history and message logs. There is an option to backup all files within your internal storage directory, usually found in ‘Back up’ section of your settings.

You can explicitly back up data one category at a time as well, such as for photos and videos you could upload them to Google Photos or Dropbox as backup (go with compressed sizes if you have data limitations), with the latter working for other files as well. Messaging/social apps have a backup feature as well. Ensure all of your personal data is backed up and you haven’t missed anything.

• Account management - Go to Settings > Accounts and from the list of accounts shown, make sure to remove each one of them. For my case, I had one Google account (one may have multiples) and other accounts such as a messenger account. I like to sign out from my Google apps (+ the Google sign-in on chrome via Android) and then remove my Gmail account. For extra safety and cross-checking purposes, I created a temporary new Gmail account and set that to the phone’s default google account, ensuring no trace of my old primary google account prevailed.

Furthermore, don’t forget to check your game settings from Google play games as well wherein most games use google play games to sync game account data + store purchase card information. For extra safety, I removed Payment methods from my google play account as well since I didn’t need prompts to use card data for my in-game purchases; although removing your google account was all that’s necessary as the game needs to be able to access your google play games account via google account during the loading phase. Going the extra mile here might be helpful as you might have saved payment card information in your browsers’ via the ‘save card option’ as well.

Moving onto the other, considerably less complicated accounts such as ones that require your number (like Uber and Swiggy accounts), a simple sign-out does the work. But for accounts such as the messenger account, you cannot remove it directly, which I find to be a rather inconvenience as well as insecurity on their part. I was able to look at my messenger account from the app even after deleting every account on my device and the option to remove the account in Switch Account section was not available. Apparently, you need to have another account to be signed in (or ‘switch’) in order to remove your account. Proceeding with that, I created a new account via my freshly created google account and then switched over messenger accounts, and deleted my old/primary one. Cumbersome on behalf of messenger eh?

Now head back to your google account on your new device or local PC and go to Recently Used Devices section and remove your old phone (Google maintains a clear login record such as ‘Logged in at 00:00:00 time via browser_name on device_name’) in case its present, which obviously wouldn’t be since we removed it, but just for the sake of self-satisfaction its worth to check.

• Cleansing everything - Start with trivial things like messages and call log/history, then move to deletion of all your files inside internal storage. One thing I like about Google backup and sync is that it automatically exports my contacts as per my Google account and no trace of any number that I had was there even when I had my sim (apart from regular sim-saved contacts) inside my old phone after I logged from my Google account. Undoubtedly, all of your contacts will be restored on your new handset when you set up your Google account there.
  Moving forward, delete all the extra applications you installed (if you can’t uninstall them directly, there are other methods like Disable from the application information section in Asus handsets, or uninstallation from a computer via USB debugging - plenty of videos in YT out there) after subsequent log-outs from each of them.

• Adding junk for memory writes - This brings up the topic of file recovery which can be explicitly done by the new owner of your old device if they have a knack for how memory works; check this post to understand better. Upload some random files which do not correlate to you or your historical data. For my 64GB storage space, I transferred ~50GB of useless large chunks of files (faster to copy) including some big video files as well. I deleted them, and then again re-copied them - which may sound silly but actually am leaving no scope for my old data to be retrieved. After following this procedure twice, you can rest assured, as most of the retrievable data in your internal memory is your copied junk that you have recently deleted. Keep the files (copy twice, delete once) after the second copy as you’ll proceed to factory reset keeping those files next.

• Factory Reset - You’re finally ready for the final step! Hit the Factory Data Reset inside settings and sit back, relaxing for a while till it gets done. Note: In case you’d like to provide your phone right after a Factory Reset, ensure you disable Factory Reset protection or simply don’t use any screen looks such as patterns, numbers, or biometric fingerprints.

For the sake of extra safety, you may consider the last step again, adding new junk files to your old phone after the factory reset and deleting them, which virtually makes all of your retrievable data the new dummy files you have been deleting :)

Note: For smartphones coming with the issue of a dead touchscreen and display combined with USB debugging turned off, I’ve found (coming from a bit of research on the net) that data retrieval can be achieved in these ways:

• Using a suitable USB hub (C/A based on your phone’s port), a mouse with a USB connection (wired/wireless/whatever), and an HDMI cable (C/A based on the hub’s ports). Plug the HDMI end to a TV or display device that can map your phone’s display, and then use the mouse to enable USB debugging through click-navigation. (Keyboard would have been a choice too, but that’s not suited for drawing patterns which can be the security measure for some)
• Using adb on clockword mode (to avoid resetting, while trying to bypass the ‘unauthorized’ status for devices with USB debugging turned off) or manually injecting device drivers that bypass the phone unlock security.
• Replacing the screen (however costly as it may be), assuming the phone’s internals are still intact.

Anirban

02/20/2020