The green/red dot next to Arm/Bypass buttons IS NOT the indication whether the sensor is armed or not! It shows the current tripped state of the sensor - Green=Idle, Red=Tripped.
The only indication whether the sensor is armed or not is to check which button (Arm or Bypass) is highlighted in blue.
Pretty much all sensors go from green to red (i.e. tripped) almost instantly - motion detected, door/window open, water leak detected etc.
But going back from red to green (i.e. "untripped", reset or go back to idle) is another story. Some sensors need to be manually reset (water leak sensors, like FortrezZ), some get untripped instantly (door/window closed) or some take time to idle-out (motion sensor when it does not detect motion for some period of time, like 20 minutes by default in HSM100).
Note: The default idle value of 20 minutes in HSM100 can be changed, see ExpressControls3in1)