Touch Screen Test

How to test a touch screen

1. Open this page on the phone, tablet or touch laptop you want to check and press Full screen so the test area covers the whole display, edges included.
2. Touch the area with one finger, then two, then as many as you can. Each contact gets its own colour, a circle and a number, and Active touches shows how many the screen sees right now.
3. Drag your fingers slowly across the screen. The trail stays visible, so a break in a line shows a spot where the digitizer lost your finger.
4. For a systematic check, choose Grid coverage in Mode. Swipe over every cell until the whole screen is green. Tick Highlight untouched cells to see the remaining gaps in red.
5. Press Clear to start again and Exit full screen (or the Escape key) to leave.

What the results mean

Active touches is the number of fingers currently on the glass and Max simultaneous the highest number seen since the last Clear. Most phones and tablets track 5 to 10 points; many touch laptops report 10. Reported touch points is the value the browser announces through navigator.maxTouchPoints. If you can never reach it, some fingers are being merged or dropped; a result of 0 means the browser doesn’t see a touch screen at all.

Total contacts counts every touch-down since the last reset. Current contacts lists each finger with its order number, its pointer id (a number the browser assigns to each contact for as long as it lasts) and its position in pixels.

Pressure and Contact size come from the Pointer Events API. Many touch screens don’t measure force: browsers then report a fixed value, shown as not reported. Pens (Apple Pencil, Surface Pen, S Pen) usually report real pressure from 0 to 1. Contact size is the width and height of the touched area in CSS pixels, when the screen provides it. Last input tells you whether the last contact was a finger, a pen or a mouse.

Finding dead zones

A dead zone is an area where touches are ignored or jump elsewhere. It is usually caused by a cracked or delaminated digitizer, a badly fitted screen protector, a damaged flex cable after a repair, or moisture. Typical symptoms are a line where letters can’t be typed, or a corner that doesn’t respond.

Free drawing is the quickest check: draw straight lines across the screen in both directions, close together. A gap, a jagged line or a jump reveals the faulty zone. Grid coverage is more thorough: it only turns a cell green when a finger passes over it, and fast swipes are followed in between frames, so a cell that stays red after several passes points to a real problem. Choose a smaller Grid cell size for a finer map.

Test with a clean, dry screen and without gloves. If the problem only appears with the protector on, the protector is the cause.