SAN FRANCISCO — An aqua blue light appeared on my outstretched palm, showing a menu. Slowly, I circled my wrist to scroll, pressing an index finger and thumb together in a pinching motion to select an item. I wanted to send a text message. The device on my sweater, a 2-inch-square magnetic pin from a startup called Humane, let out a soft “clink.” I spoke, and the words leaving my mouth projected instantly into my hand. Squeezing a fist, the message sent with a “whoosh” sound. The gadget, called