Touch screen test

How the test works

Tap Start and the page goes fullscreen, covered by a grid of dark cells. Drag your finger across the screen in any pattern you like; every cell the finger passes through turns yellow. The counter in the corner shows the share of cells covered so far, and the run finishes on its own the moment every cell is painted, or when you tap the × button. The few cells under that button are left out of the count, because a finger there taps the button instead of painting. There is no time limit and there is nothing to configure except the cell size.

Start each stroke inside the screen and move outwards to reach the edges. A swipe that begins at the very edge of the glass is a system gesture on most phones (back, home, notifications) and will leave the page instead of painting.

The grid is built from the actual size of your screen when the test opens, so a phone in portrait gets a tall grid and a tablet in landscape a wide one. Three cell sizes are offered. Large cells are close to the width of a fingertip and give a quick overall check. Medium and small cells are for hunting down narrow stripes: a touch panel is a mesh of horizontal and vertical sensing lines, and when a single line fails, the dead area is only a few millimetres wide. It slips between large cells but cannot be painted with small ones.

Fast swipes are handled correctly. Browsers report a finger position only once per frame, so a quick stroke can jump several cells between two reports. The test fills in the straight line between them, which is what your finger actually did. That means a cell that stays dark after you have crossed it slowly is a real gap, not a reporting artefact.

Everything happens in your browser. The page reads touch events, the same events every website receives when you scroll, and draws on a canvas. No touch data leaves the device and nothing is stored.

What the result means

The result card shows the percentage of cells your finger managed to paint, and the context line tells you how many cells that was and at which size. Read it together with what you saw on the screen:

• 100% covered. Every part of the digitiser reported at least one touch. The panel has no permanent dead zone at this cell size.
• A few dark cells you could not paint, however you tried. That is a dead zone. Note its position: edges and corners point to a protector, a case or a cracked digitiser near the frame; a stripe across the whole screen points to a failed sensing line inside the panel.
• A whole outer row or column that stays dark on every run. Most likely the operating system, not the panel: phones reserve the outermost few millimetres for their own gestures and never pass those touches on. On an iPhone the test fills the browser page rather than the whole screen, so the strip under the home indicator is not part of the grid at all.
• Cells that paint only when you press hard or go slowly. The panel is losing sensitivity there. This often precedes a full dead zone by a few weeks.
• Cells that light up before your finger reaches them. Those are ghost touches, a different fault. Use the ghost touch test to log them with timestamps.

The percentage is only as honest as your swiping. A missed cell in the middle of a clean area is usually a missed cell, not a defect; cross it again before you decide.

What to do about a dead zone

First remove anything between your finger and the glass: the screen protector, a magnetic case, a wet or dirty surface. Restart the device with nothing plugged in, because a faulty charger or cable can inject noise into the digitiser and cause exactly this symptom, particularly on cheap chargers. If the dead zone disappears after a restart or an unplug, the panel is fine.

If the zone stays, check whether it moves. A dead area that is always in the same place is hardware: a damaged digitiser, a loose flex cable after a drop, or a hairline crack you cannot see. Software cannot repair it. A dead area that comes and goes with heat, with a specific app or with the phone in a certain position is worth a factory reset and a system update before any repair.

Replacing a digitiser is usually a whole-screen job on modern phones because the touch layer is bonded to the display. Get a quote before deciding; on a mid-range device it can be close to the value of the phone.

When to return or claim the warranty

Test a new phone or tablet on the first day, with the small cell size, before you put a protector on it. A dead zone on a new device is a manufacturing defect and any shop will exchange it inside the return window, which is far simpler than a warranty claim later. For a warranty claim, screenshot the finished grid before you tap ×, note the cell size, and describe where the dark cells are. A repeatable dead zone with no crack in the glass is covered by every manufacturer's warranty; a cracked digitiser after a drop is not, and repair shops can tell the difference under a microscope.