From The Talos Principle Wiki
An Activator.

Activators are puzzle elements that accept laser light of a specific color and then activate other puzzle elements within a given radius without the need for direct connections. In particular, they cause nearby blue doors to open and cause other nearby Activators to activate.

Like receivers, each activator accepts only light of a specific color. However, an active Activator will activate any nearby Activator regardless of the secondary activator's color.



The following puzzles use activators: