My 90+ year old mother heard a series of 5 knocks on her front door around 1am last night. She was so convinced it was someone trying to break and enter she pushed the call security button on her security system nd pushed her life alert button as well. The police came and could find nothing. The security camera on her front door showed nothing until the police arrived. She lives alone at night and is very determined to be independent and self reliant since my dad dies 11 years ago, though she does have caregivers during the day. In her life, I think she has experienced some depression from time to time, she is not very secure about herself, and I think she has episodes of sleep apnea. On occasion she gets up to pee at night 5 or more times, occasionally only once,, more often 3 or 4. She uses a rollator and has difficulty standing for very long. What might be the cause of the knocking, other than something paranormal, which she and my sister have commented they have experienced in that house, before and after my dad passed away.