There are a lot of technical problems with trying to use the current options available for presence sensing in smart things. The truth is a mesh device just probably isn’t a good idea for this. I agree that Bluetooth point to point, like an iBeacon, would likely be much more reliable. But we don’t have that right now.
What we have works pretty well if you want to, say, turn on the heat before you get home from the office, or similarly turn on some lights. Things that don’t have to be exact to the minute.
Because I need more precise timing due to the bus stop problem I’ve mentioned elsewhere, I’ve ended up adding a second type of device to shrink the geopresence zone and to handle the problem of random drop off’s.
But I personally still wouldn’t use this to trigger an alarm. I have a separate alarm system, and I do pay a monthly fee, but that’s just my personal preference. I want my alarm system to work even when the power goes out, I want it to connect to a professional monitoring service, and I want that connection to be cellular. For other people, not having a monthly fee is more important.
So there are multiple ways to look at the problem, but a lot of it does have to do with your personal preferences.