Since I needed the exact same thing when I jumped to hubitat (I relied on fibaro ubs/smart implant for quite a few things), might I (predictably) recommend nodemcu's flashed with the konnected software to do exactly what you need?
Massive fan. I've got loads of these. Way better (IMO) than my fibs ever were. And only cost about 2 quid each.
Ebay about 2 quid. Amazon about a fiver. Check out the konnected main site for great guides. =)
Post above requires the purchase of a zigbee/zwave sensor of some sort. I wanted to have sensors on multiple doors and windows without needing to purchase multiple £15-20 units. One nodemcu allows something like 7 cheap ■■■ contact sensors for pennies.
I'd look at Zigbee contact sensors. The Xiaomi Mijia and Aqara contact sensors are really small, but you have to be up for the Zigbee network requirements to keep those stable. I've not tried the new Sonoff Zigbee contact sensors, but they're really small too.
One of the community members is willing to create a driver if you'll send him a device. If you're wanting a solution that might also help others, then that's one way you could do it. If you just need an inexpensive solution for your one use case, then I'd personally try the Sonoff Zigbee contact sensors (if I didn't already have the right setup for using the Xiaomi for this purpose as I already do).
It should be in the US next year sometime. Just like the Shelly motion.... The US gets the Shelly devices well after the EU does. That said if you want the driver before I can get the device you can always send those devices we don't have yet to me.
Just having a look at the nodemcu. All new to me.
What's the reason for using the Konnected firmware (and presumably Konnected drivers in Hubitat). Is it better/simpler than Hubduino or have I misunderstood.
I started on smartthings and became familiar with the konnected software then. Purely for familiarity for me.
I think the Hubduino sounds amazing and definitely more flexible (you can do pretty much anything, which is something I intend to look into once I start playing with servos etc).
But for me, konnected was virtually an off-the-shelf product.... Or at least close to. Buy a nodemcu, a dc psu, handful of breadboard wires for simplicity and if you feel the need, grab a few 3v relays.
My current use for these little sods ranges from multiple standard magnetic contact sensors (cheap as chips!), some 12v honeywell pir's scatered around the house (6 quid and work FAR, FAR better than my battery powered, 20 quid smartthings motion sensors), ds18b20 sensors for the Hottub, dht22's in every room for temp sensing and humidity (Bathroom), and the relays controlling 2 wire thermal actuators to open/close my240v radiator valves (with webcore and a cheap zwave boiler switch... Which I'm close to replacing with another nodemcu instead to avoid zwave).
Does that help? I'm obviously a massive fan, for many great reasons. I'm always quite suprised that these don't come up in conversation more often, but I'm assuming that for whatever reason, some people aren't keen on WiFi. I know I was dead against it. U til these came along.