False motion with ST motion sensor

I have read a few posts about false motion alarms but had my first experience tonight. About 4am I got up to use the restroom. We are on the second floor and the motion sensor in question is on the first floor with absolutely no line of sight to the upstairs. As I was walking to the bathroom it triggered. It has never gone off without us being down in the room with it. We panicked obviously but eventually found nothing. No bug or fallen object either. I just found it so weird that it was when I was walking upstairs. Any ideas? I know there has been some discussion on battery life. I’ve had my system for a month and this sensor is at 88% like many of the false alarms.