How touchscreens work

An invisible grid under the glass

Look closely at a phone screen and you see only glass and a picture. Hidden between the glass and the display is a very fine grid of transparent wires, arranged in rows and columns. A small electric charge sits on this grid all the time. This design is called a capacitive touchscreen, and it is used in almost every modern phone, tablet and many laptops.

Your body conducts electricity. When your fingertip comes close to the glass, it draws a tiny amount of that charge towards it. The phone constantly measures every crossing point on the grid. Where the charge drops, it knows a finger is there.

From touch to action

1. The touch controller scans the grid many times a second.
2. It finds the spots where the charge has changed and works out the centre of each one.
3. It tracks how those spots move over time: a quick tap, a long press, a swipe or two fingers pinching.
4. The operating system turns that into an action, such as opening an app or zooming a photo.

Because the grid can sense many points at once, you can use several fingers together. That is called multi-touch, and it is what makes pinch-to-zoom possible.

Why gloves and pens often do not work

Ordinary gloves, plastic pens and long fingernails do not conduct electricity, so they do not change the charge on the grid. Touchscreen gloves have conductive thread in the fingertips. Stylus pens for phones have a conductive tip, or, in the case of more advanced pens, contain their own electronics that the screen is designed to detect.

Water can confuse the screen for the same reason: it conducts electricity, so raindrops may look like extra fingers. Many phones have a mode that copes better with wet screens, but drying the screen is the simplest fix.

The older kind: pressure screens

Some older devices, such as certain ticket machines, card terminals and car screens, use resistive touchscreens. These have two flexible layers that touch when you press. They work with any object, including gloves, but need a firmer press, feel less smooth and usually handle only one touch at a time.

When your touchscreen misbehaves

• Clean the screen with a soft, slightly damp cloth. Grease and dirt can cause missed taps.
• Remove a thick or badly fitted screen protector, which can block or confuse the signal.
• Restart the device. A software glitch can freeze the touch controller.
• Check the charger. Some cheap chargers cause electrical noise that makes the screen "jump" while charging.
• Look for cracks. Even a small crack can break the grid in one area. If touches fail in the same place every time, it may need a repair.

Tip: If parts of the screen start tapping on their own ("ghost touches"), unplug the charger, take off the case and restart. If it continues, get it checked, because it can open apps or send messages by itself.

Accessibility features worth knowing

If tapping is difficult, phones have built-in help. You can make touch less sensitive to accidental taps, change how long a press must be held, use voice control instead of touch, or turn on a floating on-screen button for common actions. Look in Settings, then Accessibility.