What type of device typically uses light to trigger activation in an IED?

Infra-red devices are commonly used in improvised explosive devices (IEDs) for activation because they rely on the emission and detection of light wavelengths that are not visible to the naked eye. When an object, such as a person or vehicle, interrupts the infrared beam, it triggers the device, leading to detonation. This method often takes advantage of sensitive sensors that can detect changes in light intensity, making them effective in various environments where other triggering mechanisms may not be feasible.

Mechanical timers, magnetic devices, and manual switches do not typically rely on light for their function. Mechanical timers use countdown mechanisms, magnetic devices may use principles of magnetism for activation, and manual switches require direct human interaction to engage. Each of these alternatives operates under different principles, emphasizing why infra-red devices are a unique and effective choice for IED activation based on light detection.