“Keep in touch” is a phrase that dates back to when communicating across a distance required effort and time. People wrote letters by hand and mailed them, and then days, weeks, or even months went by before receiving a reply. Today, cell phones, computers, and the Internet have made communication practically instantaneous. We keep in touch with each other, keep track of our schedules, our business inventories — even our pets. It took a steady flow of engineering innovation to get from that old handwritten correspondence to today's lightning-fast forms of communication.