Device Monitor How to check a used iPhone before buying it: a 10-minute checklist
Meet in daylight, get the seller to unlock the phone, install Device Monitor and run the checklist below - specs, screen, sound, sensors, touch, keyboard. Then check the stuff no app can see: battery health, part history, Activation Lock, all in Settings.
Why test a second-hand iPhone on the spot
Most faults on a used phone hide from a quick glance. A stuck pixel. A speaker that rattles. A proximity sensor that leaves the screen lit mid-call because of a cheap screen swap. Once you've paid, all of that becomes your problem. Ten minutes on the spot is the cheapest insurance you'll ever buy.
The checklist, in order
- Specs. On Monitor, open Edit Dashboard, add Device Info. Compare Model, Total Storage and RAM against the listing - RAM and storage round down to whole binary gigabytes, so a 128 GB phone reads lower than that on purpose; it's a much smaller figure than advertised you should worry about.
- Screen. Diagnostics > Screen & Display > Dead Pixel Test, brightness all the way up. Dark dots on bright colours, glowing dots on black.
- Speaker. Audio > Speaker Test: run the Frequency Sweep, listen for rattle on the low end.
- Microphone. Microphone Test > Start Test, then talk. It should reach Mic working!.
- Cameras. Camera & Biometrics > Run Camera Tests lists the hardware iOS reports - then take an actual photo with each lens in the Camera app, because this test doesn't judge image quality.
- Proximity sensor. Environment Sensors > Proximity Sensor Test: cover the top of the screen near the earpiece. Screen should go dark and the card should read NEAR.
- Compass and GPS. Open Digital Compass, turn around, the heading should follow. Then Wireless & Location > GPS Accuracy Test > Start GPS Test.
- Bluetooth. Bluetooth Scanner > Start Scanning. Nearby devices should show up with their signal strength.
- Touch. Touch & Haptics > Gesture Test: swipe all four directions in Swipe here, pinch, hold for a Long Press.
- Keyboard. Keyboard Test: type the given sentence, check every key registers.
| Check | Pass | Worry if |
|---|---|---|
| Device Info | Model and storage match the listing | A different model or a much smaller capacity |
| Dead Pixel Test | Clean colours on all five screens | Dots, lines or tinted patches |
| Speaker Test | Clean tones from 250 to 8000 Hz | Buzz, rattle or silence |
| Microphone Test | Mic working! | Level stays near 0 while you speak |
| Proximity Sensor Test | Screen off and NEAR when covered | Nothing happens when you cover the earpiece |
| GPS Accuracy Test | A fix with a few metres of accuracy outdoors | No fix at all after a minute outside |
| Bluetooth Scanner | Devices listed with a signal in dBm | Nothing found in a busy place |
| Gesture Test | Every swipe direction and the long press register | Parts of the screen that ignore touch |
What no app can check, and where to look instead
- Battery health: Settings > Battery > Battery Health. No app can read it; the battery card only shows charge level.
- Replaced parts: on recent iOS versions, Settings > General > About lists part and service history.
- Activation Lock: get the seller to sign out of their Apple Account and erase the phone in front of you. A phone still tied to someone else's account is a brick.
- Blacklisted phone: check the IMEI (Settings > General > About) against your carrier's own records.
- Water damage: only a technician can inspect the liquid contact indicators inside the phone. No app, this one included, can see them.
- Face ID or Touch ID: set up a face or fingerprint in Settings yourself. The app's own biometric test is part of Pro.
Common mistakes when buying
- Testing only on WiFi - put your own SIM in if it's sold as unlocked.
- Skipping the proximity test on a phone with a replaced screen. That's the part cheap repairs break most often.
- Treating any app's certificate as proof there's no water damage. There isn't one that can prove that.
Questions and answers
Can I run these tests without a SIM or internet?
Yes - every hardware test in this checklist runs offline. Only the ads and the Latency Test want a connection.
The RAM shown is lower than advertised. Is something wrong?
Usually nothing's wrong. iOS reports a touch less than the marketing size, and the app rounds down to whole gigabytes on top of that, so an 8 GB phone can read 7 GB. Worry only if the gap is much bigger than that.
Does the Camera Test check photo quality?
No. It only lists which camera hardware iOS reports. Take real photos with each lens in the Camera app if you want to check focus and spots.
Can the app tell me if the phone was repaired?
No - part history lives in Settings > General > About on recent iOS versions. The app can only tell you whether the repaired parts, screen and proximity sensor included, actually respond.
You might also like
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