When I come home the sensor joins the mesh and reports it's on dc and present my rule will run and open the door.
When the car is sitting in the driveway or garage, it's on battery (as noted I'm converting my BMW to be the same as our other car, USB power only when the car is running) so my rule can never run in that state, which will block any openings when the car is sitting in the garage or driveway.
@NoWon suggestion about checking the car power status a long with presence is good one to tide up the garage door automation. This will make sure that the garage does not open accidentally.
To be honest with you, handling power outage cases always worry me. I am not 100% sure the start up behavior of the hub. Again, @NoWon suggestion is solid. We should do that rule with our sensor and garage door.
At the same time, I personally minimize this downtime with UPS and battery backed up repeater. I know that this is not a solution but at least it will make it so much rarer. I do get power outage in my area from time to time (perhaps more than average American household). I do have generator and UPS.
I will pay more attention more for the power outage case. I have not seen any issue so far on my home my self. Yes, I did experience some power outage in the past. I don't have development hub anymore. It broke about a year or two ago. I will try to get another one on next sale. Once, I have one, I can simulate power outage and test what would be the behavior.
@danabw, sorry not to give you the credit for the excellent idea. I was not feeling too well last night and slept early. I have too many thing to catch up in the morning.
If an outdoor repeater is a little difficult to manage I highly recommend the Sonoff USB zigbee dongle, and the tiny Tuya USB repeaters.
Via the SonOff or the Tuya (depending on which the Arrival Sensor seems to see first) and a mid-size antenna on the Arrival Sensor I'm getting the garage door opening just as I hit the foot of my driveway. That's 55' from the Tuya behind my dual-wall metal garage door, and when it hooks up to the SonOff that's 75' away from the foot of my driveway through the garage door and two walls.
@danabw
Which driver are you using with your Sonoff usb dongle?
Have 2 sitting on my desk I just never got around to pairing with my hub.
I was going to try them with home assistant but never did.
I am using Xbee3 pro as routers (and end devices) with 20 foot long cable outside through the attic and a roof vent onto my garage roof.
Xbee3 pro's are rated up to 2 miles. But this is limited to antennas on both ends (and antenna placement) as well local interference, as well as how often the arrival device is transmitting (most are every 10-20 seconds) and how fast you are driving. You can move quit far in 10-20 seconds.
Mine usually trigger about 2-3 houses away.
I believe @iharyadi arrival sensors are about the same power level as the Xbee3 pro.
They tend to join as a "Device" but then they log endlessly. Based on advice from @aaiyar I changed them to the Ikea repeater driver and they work w/out issue using that.
That would not fly for my use...my wife would freak out. She is very conservative about automations related to doors/locks.
I've "tuned" my arrival sensor setup (via changing antenna to the mid-sized one) to respond at the bottom of the driveway so she won't worry about them opening the door when she's not actually right at the house. We have a long enough driveway (about 45', and uphill) so that is plenty early for her arrival home.
@danabw looking at the Sonoff specs it has a +5 to +20dBm settable output
The Xbee3 pro is +19dBM @ 135mA.
So the Sonoff is likely rated the same range or more as the Xbee3 pro.
300ft (indoor) to 2mile (outdoor) range.
Looks like the ZBdongle-P default is +5dBm but the ZBdongle-E default is +20 dBm
Need another myself but waiting till he does usb-c
It's definitely a great device. I recommend them when i can. I hope he's making at least some profit on these. He should also sell them on the ST forum
What stubby antenna did you use?
Looking to replace my SmartThings arrival sensor that is in my son's backpack with iharyadi's arrival sensor. Tired of SmartThings randomly going departed and then coming back (have 3 all doing the same thing). iharyadi's arrival sensor and my Xbee3 have never had a problem.
And yes, that is very high praise, 
She is very conservative about automations related to doors/locks.
