Wanted: One Doorbell

A sheriff's deputy knocked on our front door Saturday night.  My daughter and I answered the door.  "Did someone call 911?" he asked.  "Oh, yes, no, I didn't mean to, I was trying to dial 919 area code to North Carolina, but I must have pressed 911, yes, I've done this before, I didn't mean to," I answered.  Then the deputy asked who else was home.  I told him my husband was upstairs.  He looked at me and asked, "You're sure everything is all right?"  I told him yes and started apologizing profusely for wasting his time.  You know he walked away thinking, "What a dingbat." 

But, he knocked.  Why?  We have no doorbell at this time.  Just this: