[Geezer1]

Thanks for the all the help!

You're welcome! I've noticed activity on this forum has recently fallen - might be due to XMAS.

Finding adequate "free" electrical diagrams might be a stretch. You can get them from Toyota for a small fee at https://techinfo.toyota.com/

The following web page has links to diagnosis information about the anti-theft system: Sitemap

I can view a bazillion electrical diagrams for the 2011 Sienna Limited including 19 diagram files for the anti-theft system on the "Auto Repair Source" service available through my local public library's website. It's not realistic for me to download and upload all these files. Maybe your public library offers a similar service.

The first components I'd check would be the switches on the door jams. They are of a type that are known to sometimes fail and which Toyota stopped using on their more expensive cars (e.g. Lexus) around 25 years ago. An intermittent problem with one these switches could set off your alarm. Press each switch with a finger to see if they operate smoothly. If the little "piston" in the switch binds or is sloppy, that could indicate a failure. There have been threads on this forum about replacing them. I replaced a very similar switch on an early Lexus in the 1990's and it was fairly easy but did require removal of interior trim to get to it.