As you are probably aware from my questions, my background is not in electrical design. All your comments are appreciated and most welcome. Having followed your posts ... it seems you are a very active member of the forum.
There are a lot of terms and new techniques for me to digest. Let me do my homework, and I will resubmit if you are willing to humor an old man learning new tricks.
I think you are right ... the contactor is not needed ... just look for power "off" from the native power ... and let the other power connector with the UPS handle the MKR 1000 and all the peripherals. I just need the UPS to work long enough to send a message indicating a problem has occurred, and maybe keep the "buzzer" active to draw some attention.
The "resistive divider" I assume is the same as a "voltage divider" ( a series of resisters to drop voltage)? Is the 100 ohm resister your suggesting from ground to D8 (the input pin) acting as a "pull down" resister. And the 68 ohm resister is the "resistive divider" to drop the 5V to approx 2.4V?
Have never worked with transistors ... so I am going to have to do some work before I can ask intelligent questions, but I think I will start with the "model of a simple switch" where the "base" receives a low current which allows a larger current to flow from the collector to emitter.
So my assumption at this time is connect the low voltage from an output pin (using the "set high" command) to the base of the transistor, and allow the greater current (5v) to flow from the collector through to the emitter. From there to the + buzzer, and back to ground.
I am attaching a part of the data sheet from Jameco for the 2n2222 which you mentioned. I just need to figure out what all the information means. If I am reading this correctly the information I need to understand is in the "On Characteristics" section.
I am using a Piezo buzzer running at 3 - 15 VDC ... drawing 10 mA at 12V. (Jameco part #2117430). 90 db is nice and loud, but the lower voltage will probably result in a lower sound volume.
I will try to deal with the "power supply" bypass when my head is a little clearer.
Thanks again -