EMZETT.Securely erasing drives before passing on devices
In short: Normal deleting and formatting does not really remove data; for passing on or selling you need encryption, overwriting or a factory reset with erase function.
In more detail: Whoever sells, gives away or disposes of an old phone, laptop or hard drive often unintentionally passes on photos, passwords and documents. “Deleting” in the recycle bin or a quick format removes only the entry in the table of contents; the data remains readable until overwritten.
In Depth
Beforehand
- Back up the data you want to keep.
- Sign out of accounts and unlink devices (Apple ID, Google account, “Find My Device”, activation lock, Microsoft account, licences, game accounts, cloud services).
- Remove cards (SIM, microSD).
- Unpair smartwatches/headphones.
Smartphones and tablets
Modern devices are encrypted by default. A factory reset (Settings → Reset) deletes the key and makes the data practically unreadable. On iPhone: “Erase All Content and Settings”. On Android: check encryption, then reset; remove the account first. With very old devices encrypt first, then reset.
Computers, hard drives and SSDs
- HDD: a single complete overwrite is usually enough today (
shred,dd if=/dev/zero, tools such as DBAN/nwipe, Windows “Reset → Clean the drive”, macOS Disk Utility). - SSD: overwriting is unreliable because of wear leveling. Use the manufacturer’s Secure Erase / ATA Secure Erase / NVMe Sanitize (for example with the manufacturer’s tool or
nvme format --ses) or better still: the drive was encrypted from the start (BitLocker, FileVault, LUKS) – then it suffices to destroy the key (crypto erase). - The operating system is to be reinstalled or reset.
- Treat external drives, USB sticks and SD cards likewise.
Defective drives and disposal
Drives that no longer work can be mechanically destroyed (drill/smash hard drive, scratch platters, break SSD chips) or destroyed by certified service providers (DIN 66399 security levels). Companies must document this. Electronic waste belongs at the recycling centre/take-back, not in household waste. When passing on to family a reset suffices; for sensitive data (company, tax, health) use stricter procedures.
See also: Backup strategy, Drive and SSD health, Wear levelling, SSDs