What you need is: - Device running home assistant. (Raspberry Pi, old computer, or something purpose built like Home Assistant Yellow - A Z-Wave/ZigBee/Matter controller. I believe the home assistant yellow has a version that has this built in? - A door sensor that matches your controller's protocol. (ZWave ZigBee, Matter) - A smart plug that supports Home Assistant, that matches your controller's protocol or is WiFi based (Kasa brands are good imo and easy to get to work. WiFi based too) - A cheap siren from Amazon (here's mine) - A power brick for the siren. Check the often purchased with section. - Google Home/Alexa speakers. - Time.

My setup is a "I have this so I'll use this" setup. I wouldn't suggest someone going out and buying it for this purpose.

I would not suggest getting Z Wave at this point either, like I have. It appears it's on a decline as far as manufactures supporting it, and each module is getting more expensive. I'd either go ZigBee or the newer Matter devices. Matter is going to take over in the next few years IMO.

Home Assistant is running my automations, integrated with Vera (Z-Wave controller for sensors and lights, discontinued), Unifi Protect (cameras that integrate awesome with Home Assistant. They have like 25 sensors per camera that you can trigger things from), Google Home (room speakers), Kasa (smart plug) +++ more unrelated.