Illustration of Nir Eyal’s habit-forming book
Credit: Nir Eyal

A middle-aged woman sits before a computer screen on the 11th floor of Expedia’s glass-clad headquarters in Seattle. Two electrodes are taped to her brow just above her left eye, two more on her left cheek. A one-way mirror reflects her face as she responds to requests issuing from a speaker mounted in the ceiling.

Behind the glass, a researcher directs the test subject as a half-dozen designers, engineers, and executives look on in rapt silence. “Okay, Shannon,” the researcher says. “Go to Expedia and start shopping for your trip to Hawaii.” The audience gazes intently at a large video display. A running graph of the electrodes’ output trails across the screen. The electrodes on the brow measure contraction of the muscles that activate frowning—a sign, according to the theory of facial electromyography, of concentration, tension, or irritation. Those on the cheek track the play of muscles involved in smiling, evidence of the warm glow of delight that occurs when […]