"Motion Error: Downstairs Motion Not Responding"

The Motion Sensors have brackets - which are what the adhesive strips are attached to (not the sensor itself). Slide the sensor off of the bracket by pulling up on the sensor portion. The bracket will remain, but it will then allow you to access the battery and sensitivity settings switch.

I experienced the same error (just once) after upgrading from SS2 to SS3. It occurred approximately one month after installation, and in my case, it was the battery. It was not a low battery, I just removed the battery and put it back in, and it cleared the error. I have not had a problem since.

By the way, it is in no way a basic/dumb question.

Sometimes it's the battery, sometimes it's necessary to "re-seat" the battery - but other times, it could be a range problem (too far away from the base station, or, interference such as wireless signals, appliances, thick walls, etc).  If changing the battery, or re-seating the battery doesn't resolve the error, and if it occurs again shortly after (within a few days), it could be interference or even a defective sensor - in which, time to call SS to troubleshoot/request replacement.