Creepy

I just woke up at a sound that sounded a little like knocking at my front door (three quick, light taps).  When I came out to the living room, there was a glow just around the corner of my mantlepiece.  The electric candle that I keep there, and have not touched in years, was lit.  I wondered if it had gone haywire; would I need to remove the battery?  But I picked it up to turn it off, and it turned off easily at the press of the switch.  The door is locked and all otherwise seems quiet and undisturbed.