Wiping a computer or drive before it leaves the house
Deleting files and emptying the trash doesn't remove them. A device needs to be properly erased before it goes to anyone else.
What's usually going on
Until a drive is properly erased, much of what was on it can be recovered by whoever has it next. A quick format doesn't fix that either. The built-in erase tools do, if they're used in the right order.
Worth trying first
Back up first.
Erasing is permanent. Open a few files from the backup to confirm it actually works before going any further.
Sign out.
On a Mac, sign out of your Apple Account and turn off Find My. On Windows, sign out of your Microsoft account. Otherwise the device stays tied to you, and the next owner may be locked out.
Use the built-in erase.
On a recent Mac: System Settings, General, Transfer or Reset, Erase All Content and Settings. On Windows: Settings, System, Recovery, Reset this PC, Remove everything, and switch on the option to clean the drive.
Treat external drives separately.
A drive you plug in is erased with Disk Utility on a Mac, or a full format, not a quick one, on Windows. For solid-state drives, the manufacturer's secure erase tool is the safer route.
When to hand it over
If the computer won't start, the drive is failing, what's on it is sensitive, or you'd simply like someone to be sure. We can also move everything to the new machine first.
Your own technologist, on call.
Tell us a little about your setup. We'll take it from there.