Touch screen test: dead zones and ghost touches

When to test the touchscreen

Test touch when you look at a used phone or tablet, after a screen or glass replacement, and when the device starts tapping on its own. Dead zones tend to sit along the edges and in corners, which a quick try-out rarely reaches, so fill the whole grid.

Common faults and their causes

• Dead zones: a drop that cracked the touch layer under the glass, or a loose touch cable after the device was opened.
• Ghost touches (the device taps or swipes by itself): a poor replacement screen, interference from a cheap charger, or moisture inside.
• Edges that don't respond: a thick screen protector or case pressing on the edge. Remove it and try again before calling it a fault.

What to do if you find a fault

• Unplug the charger, dry your hands and the screen, and test again to rule out interference.
• If the same area still fails, it's a hardware fault. On a used device, weigh it carefully: a new screen is usually the most expensive phone repair.
• Also run the multi-touch test. If the screen was just replaced, see checking a device after a repair.