Internet connection vs cellular

You raise an interesting point. Not that I would cut my internet cable coming into the house, but I did unplug my cable modem only. There were no notifications as my wireless router was still on. I walked over to disarm my alarm, and to my surprise minutes later it did register on the timeline with a delay, but there was still no notification. I'm not going to set off my alarm, but I figure if the disarm function registered on the timeline, I think that the monitoring company would still be notified. When I plugged in the cable modem, all normal operation of the alarm system resumed.

I was told by a SS rep. some time ago that cellular connectivity is always the "default" for the system, as far as maintaining comms with the monitoring service.  The wifi connectivity is mainly for OTA updates, managing devices from the site or your phone, etc.  He made it sound like wifi was backup connectivity for monitoring service comms.

If the foregoing is true, then the test of unplugging the cable modem (or otherwise losing ISP internet) would have no affect to the system, assuming cell connectivity was good.

^ that is what SS sold us all on, back in 2018.  However, the opposite is true - the system is designed for wifi primarily, and cellular as backup. (although, those without wifi, can of course, still use cellular-only - but in order to get OTA updates, they'd have to have a wifi connection, such as taking their base and keypad(s) to a friend or family member's home with wifi).