"I could build this in Home Assistant myself."
You can build the trigger - that part stays yours. What you'd still be building is reliable SMS and voice delivery, escalation with acknowledgment, a false-alarm window, and consent handling - and then maintaining it forever. We manage that layer so a real emergency never hits a bug you shipped at 1am.
"Is this monitoring? Will someone respond?"
It's your people, not a call center - alerted in seconds, escalated if the first person misses it. That is deliberately different from monitoring: the people who actually know your home decide what happens next.
"Open - so it's open source and free?"
Open ecosystem: it works with any hardware and nothing locks you in. The Home Assistant integration and SDKs are open source; the hosted service is the paid part.
"How do I know it will actually work?"
Test it tonight. Test mode runs your real policy on its real timeline and records exactly who would have been reached - then flip to live and trip it once for real. Your own phone ringing is the proof.
"Do my contacts need to install anything?"
No. Alerts arrive as normal texts, calls, and email, and acknowledging is one tap on a link. Every contact consents before they can be alerted, and they can always opt out.
"What happens if I outgrow Free?"
Nothing breaks and nothing is deleted. Upgrade when a single text to three people stops being a response plan - that is usually the moment you want escalation and a phone call.