How to Test a Used Phone Before Buying: A 10-Minute Checklist

A used phone can be a great deal — or a slow-motion disappointment. The difference usually comes down to ten minutes of testing before you hand over the money. Most hardware faults are easy to spot if you know where to look, and every check below runs in the phone's own browser, so you can do the whole inspection on the spot with no apps to install.

Before you start: the physical once-over

Begin with the things no test can measure. Look along every edge for dents and bend marks — a bent frame often means the phone was sat on or dropped hard, which stresses the battery and display connectors. Check the screws (if visible) for tool marks that suggest a non-official repair, and peek into the charging port for corrosion, which points to water exposure. None of these is automatically a deal-breaker, but each one should lower the price.

1. Screen: dead pixels and burn-in

Open the dead pixel test and cycle through the full-screen colors. You're looking for three things: dead pixels (dots that stay black on every color), stuck pixels (dots locked on one color), and burn-in— ghostly outlines of a keyboard or status bar that stay visible on the solid gray screen. Burn-in is common on OLED phones that spent years showing the same navigation bar, and it never gets better. Turn the brightness up and check in a shaded spot if you're outdoors.

2. Touch: dead zones and ghost touches

A cracked digitizer can look fine while a strip of the screen ignores your finger. Open the touch screen test and slowly drag across the whole surface in a zigzag. The trail should be continuous — any gap is a dead zone. Then leave your finger off the screen for a few seconds: if the counter registers touches on its own (“ghost touches”), the digitizer is failing. Finally, put down five fingers at once to confirm multi-touch works.

3. Sensors: rotation, tilt, and compass

Auto-rotate, gaming, maps, and AR all depend on the motion sensors, and a phone that took a hard fall may have a dead gyroscope even if everything else works. The gyroscope & motion test shows live orientation and accelerometer readings — tilt the phone and watch the bubble level respond. Values that jitter wildly while the phone lies flat on a table, or don't respond at all, mean sensor trouble.

4. Battery and system: what the spec sheet won't tell you

Battery health is the number-one hidden cost of a used phone. On iPhones, check Settings → Battery → Battery Health; below roughly 85% you should budget for a replacement. On Android the setting varies by maker, but the system & battery info tool shows the live charge level and charging state in the browser — plug the phone in during your inspection and confirm it actually charges and the percentage climbs. The same page confirms the screen resolution, CPU cores, and memory match what the listing claims.

5. Cameras, microphone, and speakers

Open the camera test for both front and rear cameras — look for focus hunting, dark spots on a white wall (dust inside the lens), and a frame rate that holds steady. Then the microphone test: speak and watch the level meter move; a flat line means a dead or blocked mic. Finish with the speaker test — play the left, right, and stereo tones and listen for crackle or rattle, which usually means a blown speaker or liquid damage.

Don't skip the boring checks

• Activation lock: make sure the seller signs out of their Apple/Google account in front of you. A locked phone is a paperweight.
• IMEI: dial *#06# and check the number against a blocklist checker — a blocklisted phone can't join a carrier.
• Calls and Wi-Fi: make a short call and load a website on Wi-Fi. Radios fail too.
• Buttons and ports: volume, power, mute switch, vibration, and a charging cable you brought yourself.

The two-minute version

Short on time? Prioritize in this order: activation lock → battery health → dead pixels and burn-in → touch dead zones → cameras. Those five catch the expensive problems. Everything on this list is either fine or negotiable — but only if you find it before you pay.