Which technology allows for multi-touch interactions?

Multi-touch interactions are made possible through specific technologies that can detect multiple points of contact on the screen simultaneously. Infra-red optical touch screens utilize a grid of infrared light beams that create a sensing plane. When a user touches the screen, it interrupts these beams, allowing the system to accurately determine the location and number of touch points. This capability enables advanced gestures such as pinching, zooming, and swiping, which are essential for a rich and interactive user experience on devices like smartphones and tablets.

In contrast, resistive touch screens rely on pressure to register a touch, usually responding to a single touch point at a time. Mechanical touch screens operate through physical switches, again limiting their functionality to single interactions. Simple button interfaces do not allow for any form of multi-touch, as they are designed for discrete, singular actions. Thus, the ability of infra-red optical technology to support multi-touch functionality sets it apart as the correct answer.