Touch Screen Dead Zone Test
Paint the whole area with one finger, slowly, edge to edge. Any spot your finger crossed that stays blank is a part of the screen that is not registering touch. Clear it and start over as often as you like.
How the dead-zone test works
The page records the path of your finger and draws it as a thick line. If the digitizer reports every position your finger passes over, the line is continuous. If it misses a region, the line breaks exactly where the screen lost contact — you are looking at a map of what your touchscreen can and cannot feel, drawn by your own hand.
Paint slowly. The digitizer samples at a fixed rate, so a fast swipe can leave small gaps on a perfectly healthy screen. Slow, overlapping strokes remove that false positive: a gap that survives a slow pass is real, and a gap that fills in on the next pass was just speed.
Where dead zones come from
The most common cause is not the panel at all. A tempered-glass protector with an air gap, a case lip pressing on the edge, or a droplet of water can all block touch in one strip. Peel the protector off and retest before you blame the screen. If the blank area stays in the same place with nothing on the glass, the digitizer is failing — edge and corner patches are the classic pattern, because the touch layer is bonded at the borders where stress collects.
A dead zone is also one of the few faults a shop will accept on the spot, so a photo of a clean, gaping line is worth more than a description. If the blank area moves around or only appears while charging, the cause is electrical noise rather than a physical break, and the multi-touch test is the better place to confirm it.
Frequently asked questions
What does a break in the painted line mean?
A gap your finger crossed that stays blank is an unresponsive patch of the digitizer. Small gaps can also come from moving too fast, because the screen samples at a fixed rate and a quick swipe can skip positions, so paint slowly and retest before calling it a fault.
My screen works well but one corner refuses to paint. What is that?
Corner and edge dead zones are the classic digitizer failure, and they are also what a badly fitted protector or a dented frame produces. Peel the protector off and retest. If the gap stays in the same place, it is the panel — and a blank corner is exactly the evidence a repair shop needs.
Should I use my thumb or a stylus?
A thumb or index finger is closest to real use. A stylus works too, but a very fine tip can slip through gaps a fingertip covers, so a stylus result that looks worse than your finger does not necessarily mean a fault. Test the way you actually use the phone.
Why does the line stop when I lift my finger and start again?
Each touch is drawn as a separate stroke. Lifting your finger ends the stroke and the next touch starts a new one. That is expected — the canvas shows the real path your finger took, it does not fill in the space between two separate touches.
Something is painting without me touching the screen. Is that ghost touch?
If lines appear while your hands are off the glass, yes: the digitizer is reporting contacts that are not there. The usual triggers are a cheap charger injecting noise, a swollen battery pressing on the panel, or a failing digitizer. Unplug the charger and retest — if the phantom lines stop, the cause is electrical noise rather than the screen.
Can this test detect a ghost touch problem?
Not directly. Ghost touches are the digitizer inventing contacts you never made, which is easier to see in the raw event stream than in a drawing. The multi-touch test is the better page for it: leave the screen alone and watch whether the counter rises on its own.
Does the drawing survive when I rotate the phone?
No, and that is expected. Rotating the phone changes the canvas size, which clears it. Rotate first, then paint — and use the Export image button before you rotate back if you want a record.
Is my drawing stored or uploaded?
No. The strokes live in the canvas in your browser and disappear when you reload or leave the page. Nothing is recorded, uploaded or kept.