You may not even need that. I had a 2020 Silverado. Caught myself leaving the doors unlocked a few times. I looked and one of the adjustable settings was "auto-lock", where it would automatically lock like 15 seconds after you left the vehicle. Worked great. I still usually locked it myself to keep in the habit of doing it but that way if I forgot it would lock it for me.
Oh, and it had the smart fob, push-to-start system. I tested, and it was smart enough that if you left the fob in the truck it would not auto-lock the doors. I'd test it once on purpose with a spare key fob accessible (but not near the van), but if the Sienna has auto-lock as an option, it too should be smart enough to realize the fob is in the van and not auto-lock in that case.