I have long wanted to make an interactive artwork, one that responds to and rewards the viewer's attention.  To detect a viewer's presence, I first considered a PIR sensor, a simple motion-activated on/off trigger; those are great for animated props.  But the LaserPING 2M rangefinder turned out to be the perfect sensor for this project, a proof of concept. The LaserPING does not just detect motion, it measures distance.  This allowed me to create a more nuanced response to the viewer, depending on how close they come to the artwork.  

From a disinterested distance, the quiet stack of gray squares reveals little (left/top, below)  If the viewer approaches within about 2 meters, two squares shift slightly to offer a tiny bit of color.  Take another step,  and a few more slivers appear. Lean in for a close look, and the piece rewards the viewer's interest as all the panels turn to flash peeks at the bright red base underneath (right/bottom, below).  Retreat from the piece, and the squares recompose themselves into their ordered gray arrangement, keeping its true colors hidden until once again a viewer takes a closer look.