How to find dead zones
Tap Start dead-zone test. This page uses a finer grid than the main test (cells of about 28 pixels), so a small dead spot shows up as a single dark cell instead of hiding inside a large one. Drag a finger across the screen in rows, then in columns. Every cell the finger crosses turns green even on a quick swipe, because the gaps between two touch samples are filled in.
The buttons float over the grid. Tapping them doesn’t count as a touch, so reach the cells beneath the top and bottom bars with a stroke that starts in the open grid and slides under the bar.
Reading the pattern
The shape of what stays dark says more than the percentage:
- One cell, or a small cluster, surrounded by green: a local dead spot. Note roughly where it is, for example a third of the way down on the left.
- A straight line across the whole width or height: the screen loses touches along that line. Check whether it lines up with a crack or the edge of a protector.
- A strip along one side: often a case lip or a protector edge. Test again without them before judging the screen.
- Random scattered cells that light on a second pass: missed strokes, not dead zones.
On an iPhone, Safari can’t show a page full screen, so its address bar and toolbar always cover part of the glass. Those strips can’t be tested from a web page; the grid covers everything between them.
When a spot stays dark after a restart and a clean second pass, tap Share result for a link with the coverage numbers to show a repair shop or the seller.