Yes ADT has a monthly fee. I was trying to keep out commercial home security companies out of this thread. I was looking for DIY computer based home security items. But ADT has no part in my home Apple HomeKit.
The problem with most IoT devices is when you use it across the internet. How safe is it? I like how Apple uses Homekit on the AppleTV and uses iCloud for the internet. Your AppleTV is always running so it makes a good server plat forum to run scheduling on. I also figure iCloud is fairly safe across the internet.
So are you saying you need a commercial security company to have a safe home. Is there no reason to look at products the run on your home network?
What do you mean, "How safe is it [use it across the Internet]?" What do you think is "unsafe"?
Your "AppleTV is always running" but what do you think it's connected to? The Internet.
What you're suggesting is having a telephone not connected to anything outside your own house--not much good, is it?
If you wanted a glorified buzzer for your home security, Samsung SmartThings, et al. can handle that (same thing: it's a Z-Wave and Zigbee hub that can run functions locally; Amazon Echo is Zigbee and can run some things locally but not as much I don't think) but you have to program all that and their SmartThings app is in a state of flux right now (the geniuses at Samsung thought it would be great to completely remake their app and "upgrade" everyone to the new version before it can do half the things the "old" version does.
A problem with using various IoTs is that, my experience, they tend to fail and the more vendors and pieces you cobble together, the harder it is to fix (right now my SmartLife [Tuya-based] plug goes "offline" and I only discover that when my Alexa routine tries to operate it but when I troubleshoot it, it comes back online. Is it the plug, the SmartLife app, the router [Asus POS gaming router, could very well be], Alexa, or the integration between the two?)
This is why I like Ring: it is its own platform (more secure--it's its own Z-Wave hub running things locally and has a cellular backup--I can lose power and Internet and 1. it will still work fine and 2. I will know about it immediately) and since Amazon bought Ring, it will be tightly integrated with Alexa. Additionally, Alexa Guard (when I arm the alarm) turns all seven of my Echo devices into glass-break sensors.
Based on your concerns, I think Ring (or something equivalent) is your best bet since it checks all your boxes.