Dr. Brown gives Marty some 21st century clothes in order to blend in. The first is the pair of Nike MAGs. The other item of clothing Marty must don is a jacket. It has two functions. When Marty first tries it on, the sleeves are nearly twice as long as they ought to be. After complaining that it doesnt fit, Dr. Brown reaches and pinches a blinking and beeping red LED at the base of the jacket’s zipper. In response, the sleeves retract to a proper length, the pocket flaps shrink, and the epaulettes flatten out as a synthesized voice states, “Adjusting fit.”
You might wonder why, if the jacket is designed to be properly fitted, the sleeves start at a length that would not fit any human. My answer is fashion. Later, when we see Marty Jr. in the 80s shop, one sleeve is left super long. It could be that his is busted or just that he’s disheveled, but youth fashion has often adopted Handicap Principle as markers of status and aloofness. c.f. hip hop baggy pants. No one else shows this same thing, but fashion seems very individualized in 2015(1985).
Later after Marty gets soaked in the town square reflecting pool, the red LED on the zipper begins beeping and blinking again. Marty reaches down and pinches it, and a voice announces, “Drying clothes: on,” as hidden air dryers puff the jacket around him drying his hair and the jacket. When it’s done it emits a slim beep it announces happily, “Your jacket is now dry!”
Sure, that’s pretty cool, and obviously played for the How-Wacky-Is-This joke. But the one-button interface speaks to a great deal of context awareness and capabilities for a wearable.