Infrared is electromagnetic radiation used for short-range communication. It sits between microwaves and visible light. It is invisible to the human eye but felt as heat. Remote controls use infrared. So do some wireless keyboards and older phones. It is a line-of-sight technology. It cannot pass through walls.

Infrared communication is simple and cheap. An LED emits infrared light. A photodiode detects it. The signal is modulated to carry data. IrDA was a standard for infrared data transfer in the 1990s. It was used in phones, laptops, and printers. It was replaced by Bluetooth and Wi-Fi.

Infrared characteristics

• Line of sight: requires clear path
• Short range: typically a few meters
• Low cost: simple components
• Low power: good for remotes
• Secure: hard to intercept from another room

Infrared is still used in remote controls, motion sensors, and some medical devices. It is also used in fiber optic communication at longer wavelengths. The technology is old but not obsolete. It has found niches where its limitations are advantages.