What happens when a 12-year-old gets his wish to be an adult? That's the question answered by the hit movie Big, which shows a child-man (Tom Hanks) getting a job with a toy company and hanging out at F.A.O. Schwarz, where one Saturday he runs into his boss (Robert Loggia). The two, irresistibly drawn to an oversize keyboard laid out on the toy store's floor, delight onlookers with a soft-shoe duet across the ivories, tapping out "Heart and Soul" and "Chopsticks."

It was—you should pardon the expression—a key scene in the movie, fine-tuning the friendship between employee and employer. It was also music to the ears of Remo Saraceni, the inventor of the Walking Piano. Since the movie opened, it has brought Big business to his design-manufacturing company, Techno Futures Inc. As Techno's president, Saraceni had sold only about 100 of the colossal keyboards since he created them five years ago. By this Christmas, he expects to sell 3,200.

A divorced, Italian-born vegetarian, Saraceni lives in a converted Philadelphia bank-building loft that serves as home, office and design studio—not unlike Hanks's toy-heaven apartment in Big. Many of his self-created furnishings reflect his interest in "interactive technologies," such as the red, heart-shaped sofa that thumps out a heartbeat whenever anyone sits down. "It has to do with biorhythms," says the expansive Saraceni, 52. "It's calming and friendly." The same philosophy went into the creation of the Walking Piano, an instrument that "allows us to be in harmony with all the cosmic energies," says Saraceni, sounding much like a New Age Mr. Rogers.

Unfortunately, his original Walking Piano—first spotted by the Big filmmakers at F.A.O. Schwarz—was 6½ feet long and played only one octave. "But the script was written that Tom and Robert would play 'Heart and Soul' on the piano," says the movie's director, Penny Marshall. "The one that existed at Schwarz was too small to play the notes I needed." So the obliging Saraceni made a 16-foot-long, full three-octave piano wide enough to accommodate the crazy dancing feet of Hanks and Loggia.

Both sizes are now being marketed, although their price tags are as jumbo-size as the keyboards. The short version sells for $3,500; the large one goes to the tune of $15,000. Not quite what you'd call bargain basement, although Saraceni believes the cost is just a prelude to a transcendent payoff. "When people make music on my piano," he notes, "the sounds create a joyful social energy."