Arming Motion Sensors in Home Mode

Hi, I have just purchased an alarm system with motion sensors across 2 floors in our house, contact sensors on downstairs doors and a couple of indoor cameras. I can't figure out how to configure home mode to allow the downstairs motion sensors to be armed whilst we are asleep - basically I want everything downstairs armed in case of a break in middle of the night, but the top floor is not active. The app allows me to choose which sensors to have active during home mode, but the motion ones don't trigger the alarm. This is standard functionality for every other security system I've ever had and is essential for us to feel safe at night. I'm really hoping I'm just being a bit thick rather than this option missing. Can someone help please?