A fullscreen grid that lights up under your finger. Paint the whole thing: any cell that stays dark is a spot your digitizer never reported, and cells lighting themselves are ghost touches caught in the act.
Run it
drag to paint · R resets · ✕ or Esc exits
Multi-touch is live — every finger paints and draws its own ring. On this test a two-finger tap doesn't exit (it's test input); use the ✕ button.
How to run it
Sweep your finger across the grid in overlapping rows, like mowing a lawn, until the coverage counter reads 100%. Go right to the edges and into the corners — that's where digitizers fail first.
Watch for cells that refuse to paint under a slow, firm drag. A single stubborn cell is worth a second pass; a clean strip of them that repeats after R is a dead zone.
Take your hands off the screen for ten seconds. Any cell that lights on its own is a ghost touch — retest unplugged and dry before blaming the hardware.
Press with several fingers at once and count the rings: that's your real simultaneous-touch limit.
What you're actually seeing
The grid is a map of what your digitizer reports, drawn with no smoothing or gesture processing in between — including the coalesced samples browsers batch during fast motion, so a quick flick paints a continuous trail instead of a dotted line. That makes the failure signatures easy to read: a straight dead band is a failed sensor row or column, a dead corner is usually a connector or a cheap replacement part, dropped cells only during fast swipes point at a low sampling rate, and self-painting cells are noise the sensor mistakes for your finger.
One boundary worth knowing: this tests the touch layer, not the picture under it. A screen can track perfectly and still have display faults — run the dead pixel test for the pixels themselves, and the full phone screen check before buying or selling a used device.
Usually the digitizer — the transparent sensor layer over the display — has a damaged region or a loose connector. A clean horizontal or vertical dead band is the classic signature, because digitizers are wired as rows and columns and one failed line takes its whole strip. Software can do it too: a crashed app or an aggressive screen protector. Restart first, test on this grid, and if the same strip stays dark every run, it’s hardware.
What is ghost touch, and what causes it?
Touches the screen registers that you never made — on this grid, cells lighting up on their own. Common causes, roughly in order: a cheap or failing charger injecting noise (test unplugged), moisture at the glass edge, a cracked digitizer, a bulging battery pressing the panel from behind, or a poorly fitted screen protector. Unplugged and dry, persistent ghost touches mean the digitizer is failing.
How many touch points should my screen support?
Modern phones and tablets track ten; budget laptops sometimes two to five. Press several fingers at once — each live touch draws its own ring, so the number of rings you can hold on screen is the number of points your digitizer actually tracks. Gestures need at least two reliable points; more than five matters mainly for on-screen instruments and games.
My screen was just replaced — what should I check?
Aftermarket digitizers are where replacement screens cut cost, so test the whole grid, not just the middle: edges and corners fail first on cheap parts. Then hold a slow one-finger drag across the full width — the painted trail should be continuous, with no stutters or dropped cells — and try a fast flick, which exposes low sampling rates. Five minutes now is a warranty claim you can still make; the full checklist is on the phone screen test page.
Does it work with a stylus or gloves?
Capacitive styluses and touch-compatible gloves report through the same digitizer, so yes — and testing with them is worthwhile, because a worn digitizer often drops the weaker stylus signal before it drops a finger. Active pens (Apple Pencil, S Pen) use their own sensor layer; a pen problem with a healthy finger grid points at the pen system, not the touch screen.