Why A Sausage Can Do What Your Gloves Cannot

Understanding the Science Behind Touchscreens: From Sausages to Smartphones

In the winter of 2010, South Korea experienced an unusually cold season that led to an unexpected surge in snack sausage sales. The reason? People discovered that they could use sausages as a substitute for their fingers to operate their smartphones while wearing gloves. This peculiar incident raises an intriguing question: How do touchscreens actually work?

The Birth of Touchscreen Technology

The concept of touchscreen technology dates back to 1965 when the first-ever touchscreen was invented to aid British air traffic controllers in updating flight plans more efficiently. However, the technology was too cumbersome and costly for widespread use at the time. Over the subsequent decades, engineers refined this technology and experimented with different types of touchscreens, leading to the development of resistive and capacitive touchscreens, which are now the most common types.

Resistive Touchscreens: The Early Dominant Player

Resistive touchscreens, which dominated the market before the advent of the iPhone, operate on a simple principle. They consist of two layers: a clear, flexible material—usually plastic—on top and a rigid substance, like glass, at the bottom. These layers are coated with a conductive substance and separated by a thin gap. When something pushes hard enough, the layers connect, completing the electric circuit. This causes a change in voltage that the device’s software responds to. Although resistive touchscreens can be somewhat unresponsive, they are generally cheap and durable, making them ideal for industrial or mass use.

Capacitive Touchscreens: The Current Standard

With the release of the first iPhone in 2007, the majority of touchscreens transitioned to capacitive technology. Modern smartphone touchscreens typically consist of a protective, insulating glass exterior and an LCD screen at the bottom that displays the images. Between these two layers are several sheets, one of which is lined with rows of a transparent, conductive material that carries an alternating electric current. These conductive lines are separated from others and arranged as columns by a thin insulating layer. The points where these lines intersect are called nodes, which act like capacitors by storing charge.

The Role of the Human Body in Touchscreen Interaction

Capacitive touchscreens interact directly with your finger without the need for force. This is because the human body is a great conductor, constantly transmitting electric currents. About 60% of the human body is water, which is loaded with ions—atoms or molecules that have a net electrical charge. When you touch an app on your phone, your finger functions like a third electrical line. It interacts with the existing electric field, inducing a weak electric current that travels through your finger and back into the phone. This changes the amount of charge at the affected nodes, and voltage measurements along the second layer of lines tell the phone’s microprocessor which part of the screen is being touched.

The Challenge of Wet Hands and Gloves

However, using a smartphone with wet hands or while wearing gloves can be problematic. Both situations interrupt the electrical connection between your finger and the phone. If water is splashed across the screen, it might trigger many underlying nodes, causing the phone to behave as if it’s been touched in multiple places simultaneously. On the other hand, gloves are insulators, preventing the charge from going anywhere. But objects that conduct electricity about as well as your finger—like banana peels and certain processed meats—can activate the screen, a handy trick when you’re in a pinch.