Not sure why you would want to arm the motion detector in night mode as night mode is for when you are home and want the alarm to go off immediately if any of the sensors are tripped. If you really want to arm when in night mode it can be put into delay mode which will alarm but give you a countdown before the alarm actually goes off. You use to be able to do this at the touch screen but no longer. This now has to be done by Comcast. I think they can do remotely but may have to have a tech out to do it.