Science Puzzle
Why Won’t Your Phone Work with Gloves On?
On a cold day you try to answer your phone with your gloves on. You tap and tap, and nothing happens. Take a glove off and the screen responds to the lightest touch.
Why won't a touchscreen work through an ordinary glove?
The Answer
A phone screen senses the electrical effect of your finger, and wool or leather doesn't conduct electricity, so the screen can't feel a gloved finger at all.
Under the glass is a fine grid of see-through wires carrying a small electric charge, which spreads a weak electric field just above the screen. Your body is mostly salty water, so it conducts electricity a little. When a fingertip comes close, it draws a tiny amount of charge and changes the field at that spot. The phone measures every point on the grid many times a second and works out exactly where the change happened.
A glove made of wool, leather or plastic is an insulator, so the field is left undisturbed and the phone thinks nothing has touched it. Gloves made for phones have metal threads sewn into the fingertips to carry the effect through. Anything damp and salty works too, which is why people in cold places have been known to use sausages.
Older touchscreens, on early sat navs and cash machines, worked differently. They had two thin layers that had to be pressed together, so they worked with gloves, a pen or a fingernail, but they needed a firm push.
The principle: Capacitive sensing. A touchscreen detects the small change in its electric field when something that conducts, such as a finger, comes close; insulators such as wool leave the field unchanged.