Long before cell phones and answering machines my Dad was a pharmacist in a small town. He was happy to drive down to the drugstore when a customer called our home needing an after-hours refill, except on Sunday which was his recharge day. On Sundays we were instructed never to answer the phone unless it rang twice, paused, then rang again. Close family members knew the secret code; customers just learned Dad wasn't available on Sundays.