Before you sign in to anything on a used phone
The temptation with a used phone is to sign in and start restoring immediately. Resist it for half an hour. Some faults are invisible once your data is on the device, and one of the checks below is impossible to run properly after you have signed in.
The checks, in order
- Confirm it is properly reset and not locked A phone still tied to a previous account is a paperweight. It must reach the setup wizard without asking for someone else credentials.
- Check the battery health before anything else A phone at seventy per cent of its original capacity is a phone you will be charging twice a day. This is the check people skip.
- Run a screen and touch test Dead pixels and unresponsive strips at the edge do not show on a home screen with a busy wallpaper.
- Test every port, camera and speaker Two minutes. Charging port, headphone socket if there is one, both cameras, both microphones, the earpiece and the loudspeaker.
- Check for throttling under load A phone that runs fast for ninety seconds and then halves in speed has a thermal problem or a tired battery.
- Only then sign in Once your account is on it, returning it is a conversation rather than a refund.
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What to install for the checks and the first week
Shows the real chip, the real memory and the battery health figure. The fastest way to find out the phone is not the model in the advertisement.
More detail than the previous one, including sensor and storage information. Run both, because they disagree occasionally and the disagreement is informative.
A benchmark score that can be compared against the same model online. A score far below the expected one means throttling, a worn battery or a counterfeit.
Runs the processor for fifteen minutes and draws the performance curve. A cliff in that graph is the single most useful thing you can learn about a used phone.
The graphics equivalent, worth running if the phone is being bought for games.
Small, free, and tells you what the previous owner left behind in the storage.
A fuller file manager for looking in the folders the friendly one hides.
The power user choice, dual pane, and it opens archives without a second app.
Useful for the storage analysis view rather than the cleaning, which mostly is not needed.
The alternative for the same job. Ignore the alarming language and read the numbers.
Install the password manager before you sign in anywhere, not after. This is the whole point of the exercise.
Two factor codes that live on the device and export to a file you control. Moving these is the step people forget until they are locked out.
The official restore path from an old Android or a backup. Run it after the checks, never before.
The Samsung equivalent if either phone is a Galaxy. Faster over its own cable than over WiFi.
For moving large folders between phones with no cloud in the middle.
The long standing alternative for the same job, and useful when both phones are on different manufacturer ecosystems.
A third option, worth having when the other two refuse to see each other on a hotel network.
A browser that is not the preinstalled one, so you can tell manufacturer customisation from real behaviour.
Reading the results
| Reading | Acceptable | Walk away |
|---|---|---|
| Battery capacity | Above eighty five per cent of design | Below seventy five per cent |
| Throttle test curve | A gentle slope, ten to twenty per cent | A cliff in the first five minutes |
| Benchmark score | Within fifteen per cent of the model average | Half the expected score |
| Storage health | Sequential speeds near the model norm | Random writes an order of magnitude slow |
| Bootloader state | Locked, official firmware | Unlocked with an unknown build |
A phone that fails one of these can still be a fair purchase at the right price. A phone that fails two is somebody else problem being transferred to you at a discount that will not cover the repair.
Battery, throttling, screen, ports. Then the password manager and the authenticator. Then, and only then, your accounts.
Frequently asked questions
How do I know the phone is not stolen?
Check that it reaches the setup wizard with no previous account attached, and check the device identifier against a blacklist service in the country of sale. A seller unwilling to wait while you do both has told you something.
Does a replaced battery show in these apps?
Often the design capacity is reported correctly and the health figure resets, which can look like a new phone. The throttle test is harder to fake, which is why it is on the list.
Is an unlocked bootloader a problem?
For a technical buyer, no. For anyone else it means the software history is unknown and some banking apps will refuse to run.
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