Before selling, returning or passing on a smartphone, all data must be erased. Important: Remove the linked Apple or Google account first. Otherwise the device stays locked after the reset and can no longer be used by anyone.
Company smartphone: Check with it-tects first. If the device is managed (e.g. with Sophos Mobile), it-tects unenrolls it or resets it remotely.
iPhone
Back up your data: Settings › [name] › iCloud › iCloud Backup › Back Up Now.
Unpair a paired Apple Watch first (Watch app › All Watches › i › Unpair Apple Watch).
Choose Settings › [name] › Sign Out and confirm with your Apple Account password. This also turns off Find My and Activation Lock.
Choose Settings › General › Transfer or Reset iPhone › Erase All Content and Settings and confirm.
Android
Back up your data: Settings › Google › Backup › Back up now.
Open Settings › Passwords & accounts (or Accounts), select the Google account and Remove account. On Samsung devices, also remove the Samsung account.
Reset: Settings › System › Reset options › Erase all data (factory reset). On Samsung: General management › Reset › Factory data reset.
Confirm with your PIN and wait until the device restarts.
Note: Before resetting, transfer multi-factor authentication to your new smartphone, see “Transfer Microsoft Authenticator to a new smartphone”. Only delete an eSIM during the reset if you no longer need it.