To test a touch screen, open a touch test and drag your finger across the whole display. Anywhere the line breaks is a dead zone. The free touch screen test draws under your finger and tracks every touch point live, so dead spots and multi-touch problems are easy to see on a phone, tablet or touch laptop.
That is the short answer. The reason most people run this test is a suspected dead zone after a drop or a crack, so let us cover that first.
What a dead zone looks like
A dead zone is a region of the screen where touch is not picked up, even though the picture there still looks fine. You tap a button and nothing happens, or a swipe stops halfway. It usually follows a drop, a cracked digitiser, or water damage.
The test exposes it plainly. As you drag your finger, a line follows underneath. Over a healthy area the line is smooth and unbroken. Over a dead zone the line stops, then picks up again once your finger reaches working glass. Cross the same spot a few times: a true fault breaks the line in the same place every time.
How to test a touch screen
Step 1: Draw across everything
In the touch test, drag your finger over the whole area in overlapping passes, edge to edge. Do not rush. The goal is to cover every part of the surface at least once.
Step 2: Cover the edges and corners
Faults often hide at the edges, where the digitiser layer is most stressed by drops and case pressure. Run your finger right up to each edge and into each corner, where a thin dead strip is easy to miss.
Step 3: Test multi-touch
Place two, three or more fingers down at once. Each appears as its own tracked point. This confirms the screen handles the gestures that pinch-to-zoom, rotate and two-finger scroll all depend on.
Other things this catches
- A thin dead strip. Often along one edge after a drop. The line breaks only when you cross that narrow band.
- Ghost touches. Points that appear where you are not touching. A sign of a damaged or contaminated digitiser.
- A multi-touch limit. Fewer simultaneous points than your device should support, which can be a fault or a hardware cap.
Clean the screen first
Grease, dust and a thick screen protector can all mimic a dead zone. Wipe the screen with a dry cloth before you test, and if a protector is lifting at the edges, that alone can block touch there. Rule those out before you conclude the digitiser is faulty.
After the touch screen, the dead pixel test is worth a run to check the display itself, or the screen resolution tool to confirm the panel is reporting correctly.