I haven't thought about this in nearly a year. But was just browsing through the Hubitat community looking for unread topics...
What I did, which works nearly flawlessly, is to use a pressure mat and the Aeotec Door Sensor (series 7) which includes raw contact inputs to trigger open/close detection. Then wire the pressure mat into those connections and TADA! Now when either of the two cars drives over their perspective mat it will trigger a close event to HE. Then I take that 'sensor' input and wash it through a webcore piston that toggles a virtual switch. The virtual switch is named for each car (ex: Vehicle1, Vehicle2).
The practical effect is when the Vehicle is unparked, have Vehicle1 virtual switch OFF. Then when the car drives over the pressure mat the webcore piston will toggle Vehicle1 to ON. I did it this way because these pressure mats are not designed to withstand a constant pressure of more than 60lbs, however, I have found in practice that driving over them for a minimal duration (1-2 sec) doesn't 'appear' to damage the material that's is used to close connection.
The rest is up to the user. I have a rather elaborate series or Webcore pistons that controls nearly every aspect of garage automation. Obviously at the heart is this function for determining Vehicle Presence. The next part is tagging the drivers mobile device presence to the vehicle that just departed the garage to pair up vehicle/driver info that allow the mobile device to now be a vehicle tracker. There is much more, but getting off topic now....
The physical pressure mat I used is: United Security Products 901 Sealed Pressure Mat 9" X 15"
The Z-wave open/close sensor is: Aeotec Door / Window Sensor 7 Series 700
The Aeotec sensor is a bit high priced, but the battery last forever! It's also the only reliable one I have found that allows for direct wired contacts as an input.
Hope someone finds this information useful. I've had this system in operation for about a year and it's never failed to determine when a Vehicle is departing/arriving.
