I have sensor activity monitoring for multiple sensors, including motion detectors, but the motion detectors are always reporting “idle” online and I never receive notifications via the app of activity. Door/Window systems report activity just fine. My panel (quolsys) does indicate active/idle for the motion detectors in the history area, so I know the sensors are working (even when system is unarmed)
Motion detectors are not ideal for activity monitoring (if you are looking for fairly constant notifications) because there is a 1-hour delay between activated and idle on Alarm.com.
It looks like none of the motion detectors are currently selected for sensor activity notifications however.