I have a new product which is a door/window sensor beacon (link below). You can configure it different ways according to your needs, but the most common is to broadcast one uuid when closed and a different uuid when open.
You will then need to figure out how to get that data into HA. I think there are quite a few different ways, but I am definitely not an HA expert.
For my recent automatic garage door opening/closing project, I use a BLE scanning gateway to scan for my car’s beacon and also for the garage door beacon (to know the current status of the door). Then the BLE gateway publishes this scan data to an MQTT integration on the HA. Any HA automation can pick up the beacon scan results and trigger actions by subscribing to the proper MQTT topic.
For an HA-version of a home alarm, you could have one BLE gateway in some central-ish location, scanning for all of the door/window beacons installed around the house. It would then report all of that data, once per second if you use my example settings, to the HA. The BLE gateway would not need to be near the HA; just on the same wifi network. If you live in a mansion (congrats!) or have super thick walls, you might need to place more than one gateway in different locations to cover the entire property.