I'd tell you to look into sensors on doors that alert if a button isn't pressed within the home in a short span of time (so you don't get false alarms when you or a caregiver enters - and it can't be triggered outside or with the door open).

I am doing that already thanks, this is the backstop. Though if you have a brand/model of door sensor you used and were happy with I'd like to hear about that too.

* There are "notify you when your child/parent/dog leaves a certain area" commercial solutions, but they all seem to rely on GPS, and hence include hefty ($20-$40) monthly charges. They are essentially just little screen-less mobile phones, with all that entails (SIM, data plan, frequent recharging). Since this use case doesn't need GPS, these seem like overkill.

* Some articles[0] seem to suggest that there is such a thing as an active RFID tag that broadcasts a beacon signal over WIFI. That would be perfect - unfortunately, all I can find on "wifi rfid rtls" is sales brochures from the manufacturers of big integrated solutions for industrial applications. Active RFID tags can be bought in small batches from Alibaba, but I haven't figured out how to figure out which ones can use wifi, what equipment is used to program them, or whether they require custom wifi APs or not.

* Another option would be a non-RFID IoT device, like the Amazon IoT button[1]. I have one of those, it works great, but it's predicated on the idea of "you click the button, it does something" functionality. I don't think it's possible to give it beacon type behavior (hitting an endpoint every X seconds instead of only when the button is pressed). A similar but more hackable competitor to the Amazon button might work, but I haven't found one.

* I guess the last option would be a miniature general purpose computer, like a Raspberry Pi, which would definitely work but also seems like overkill in terms of complexity, power usage, and size. If this is the only viable option I will probably just hope the alarms on the doors are enough.

Thanks in advance for any ideas or info!

0: https://www.technologyfirst.org/magazines/2015/21-august/106... - "A beaconing active tag is most often used in RFID over Wi-Fi for Real-Time Location System, RTLS. This type of tag sends a short message at a pre-programmed interval to provide location updates"

1: https://www.amazon.com/AWS-IoT-Button-2nd-Generation/dp/B01K...