I have installed the Zone Motion Manager app via the IDE (below). There is an option within this app to create a False Motion Reduction Zone. So for example I included my Living Room ST motion sensor and my Living Room Arlo camera in this zone. If motion is detected by both sensors within one minute it will set the zone active. This zone appears to the Smart Home Monitor as a motion detector. So instead of including the sensors individually when setting up the SHM I just include the Living Room zone. So the SHM will only trigger an alarm if both the ST motion sensor and Arlo camera detects motion.
If you have more sensors (4 for example) you can set the zone so perhaps if 3 sensors activated within the time frame it would make the zone go active. This way if one sensor doesn’t pick up the motion the others will (hopefully) and the zone will still activate the SHM alarm.
It has eliminated the problem of random alarm activations caused by the ST motion sensor. You need to ensure that the Arlo cameras are activated when you run your goodbye routine or set the SHM to armed away.