Touch Screen Test
Draw across the whole screen to find spots that don't respond, and see how many fingers register at once.
No permissions. A touch screen, obviously.
Drag across every part of the screen. Gaps in the line are dead zones. Use several fingers to test multi-touch.
Each finger draws in its own color. "Hardware max" is what the device advertises (most phones 5-10); "most at once" is what actually registered. A mouse or trackpad also draws here, so on a laptop the count says nothing about the touch screen unless you use your finger.
Frequently Asked Questions
How do I find a dead zone?
Go full screen and drag a finger slowly across the entire surface in rows, then columns. Anywhere the line breaks while your finger stays on the glass is an area the digitizer isn't reading. Edges and corners are the most common spots.
What does "most at once" tell me?
How many simultaneous touches actually registered. Phones typically support 5 to 10; if you can only ever get 1 or 2 to draw at the same time on a device that advertises more, the digitizer or its driver is at fault.
The line jumps or draws where I'm not touching.
Ghost touches -- usually a damaged digitizer, a poorly fitted screen protector, moisture, or a charger with a noisy ground. Unplug the charger and retry before assuming hardware damage.