Homemade. It's a standard garage door opener, but I wired it into a relay and connected that to a Raspberry Pi and setup HAP-NodeJS. Extremely reliable, and very cost-effective. HAP-NodeJS even sends notifications from the sensor so HomeKit will send a notification if the door is opened outside of Siri (which is rare now, because it's too cool).
There's probably some good YouTube videos if interested. More than happy to share the code I ended up writing too, and wiring should be pretty trivial.