When we moved in here several years ago, the house did not have a working doorbell, it was something I was used to having, so we bought a doorbell that attached to the front door jamb but plugged into an electrical outlet. It seemed simple but what followed was strange. The doorbell would ring when there was no one there. The dogs would bark and carry on, rush to the front door and nothing. It happened at all times of the day and night, with no discernible cause or pattern. We tried different outlets, same result, without warning the doorbell would ring and no one would be there.
This began the girls believing the house was haunted. I told them that if it wasn't plugged in then rang, they should begin to worry...That thankfully never happened, at least not yet.