sensor (noun)

1. The artist installed a sensor in the painting that detected the viewer's presence and changed the colors accordingly.

2. In the science fiction story, the protagonist used a sensor to detect invisible aliens lurking in the shadows.

3. The smart home design included sensors that adjusted the lighting and temperature based on the occupants' preferences and movements.

4. In the comic book, the superhero's suit was equipped with a sensor that alerted him to nearby danger.