The tl;dr of it is if you haven’t seen any indication that someone is home, yet the egress points (i.e. external doors) haven’t opened then assume someone is still home. It gets its name from the idea that if you put a wasp in a box, and the wasp goes silent, assume the wasp is still in there unless you opened the lid.
If you have Android devices, you can also track those down to the room level using FIND.
