You unhook, roll out of the site, and before you have reached the main road the phone buzzes: the hub is offline. It does that every single time, you have learned to ignore it, and nine trips out of ten you are right to. The tenth time it is telling you something you would rather have known in October.
Two very different things produce that same alert. The campground Wi-Fi fell out of range a few hundred feet down the road — expected, harmless, and the hub keeps reading and logging the entire drive. Or the hub is plugged into an accessory outlet that is switched with the ignition, and it lost power the instant you turned the key.
The second one is not harmless. It means every drive is a blind gap in the record, and it means the battery disconnect you throw before storage kills your monitoring for the whole winter. It is worth ten minutes to know which one you have.
The two-minute test that ends the question
Nothing further down this page beats it, and it costs nothing. Open the hub screen on your phone while standing at the rig, turn the key, and watch. If the hub is still there thirty seconds later, the outlet is unswitched and your departure alerts are only ever the Wi-Fi. If it goes, you have found a switched outlet while parked in a campsite instead of in February.
Then do the same thing with the battery disconnect, because the two are separate circuits and a hub can easily survive one and not the other. That is the pair of tests we would run on the day the hub is installed, before anything else on this page becomes relevant.
Reading it after the fact
a. The backlog on arrival
Park somewhere with Wi-Fi or turn on a hotspot, and the hub reconnects and uploads everything it recorded while it was away. If the drive is there in the history, the hub had power all the way and it was only the Wi-Fi. If there is nothing at all between departure and arrival, the hub had no power, so the outlet is switched.
This is as close to proof as you get without doing the key test, because a hub with no power logged nothing and that absence is the whole signal. The backlog drains at 1,000 readings a minute and nothing in it expires, so a long drive costs you a couple of minutes of catching up and no data at all.
b. Tire caps, on a towable
TPMS caps are the best witness on a trailer, because they are the one sensor guaranteed to change while you drive. Tires warm as they roll and the pressure climbs with them, roughly a psi for every ten degrees, so a rising line through the drive is the hub saying it was awake and listening the whole time. They report every 60 seconds and the readings come back in the backlog like everything else.
The caveat is worth knowing before you buy: our rule matches caps whose advertised name begins with TPMS, and a cap sold under a different name is never recognized even when the internals are identical. So no readings does not prove the hub was off — it may only mean the caps were never being read. Check them on a stationary rig first, and see the TPMS guide for what these are and are not good for.
c. The key-on signature, on a motorhome
Turning the key puts the alternator on the house bank, and a battery monitor writes that into the record. On lead-acid the voltage jumps to a charging level — 13.8 to 14.4 volts is typical — and a SmartShunt shows current going positive. If the last frame before the hub went quiet shows charging, the engine was running when the hub died, which means the outlet is ignition-switched. If the last frame shows the bank sitting at rest, the hub outlived the key and it was the Wi-Fi.
Three things narrow this. Morning sun does the same thing to voltage that an alternator does, so check the clock before believing it. A lithium bank barely moves its voltage at all, so use the shunt’s current sign instead — a Lancol reads voltage only and has no sign to give you. And a towable shows nothing when the truck starts unless it has a charge line through the 7-pin, which plenty do not.
d. A cab door, as a supporting clue
A motorhome again, and the weakest of the four. A Shelly BLU Door/Window on the driver’s door reports open and closed every 60 seconds, and a door event a minute before the hub went quiet means somebody sat in the driver’s seat, which is when keys get turned. On a towable the tow vehicle’s doors are outside the hub’s range and there is nothing to read. On its own it proves nothing — people open doors for every reason there is — but next to a charging signature it turns a maybe into a yes.
The combinations
- Offline the instant the key turned, no backlog on arrival, last frame showed charging — an ignition-switched outlet, confirmed three ways. Move the hub.
- Offline a minute or two after rolling, full backlog on arrival, tire pressures climbing through the drive — nothing to fix. The hub logged the whole trip and only the campground’s Wi-Fi went missing.
- Offline on departure and still offline days later at a site with good Wi-Fi — this is not the drive at all. Read it as an ordinary offline hub and start with the battery.
What to do about a switched outlet
Move the hub to an unswitched outlet, or wire it directly to the house battery through a fuse. That is the entire fix, it is permanent, and it is the same wiring decision that keeps the hub alive through a shore power outage. Power and connectivity covers all three ways of powering it and what each one survives.
A hotspot does not fix this. Bringing your own connection turns the drive into a non-event when the problem is Wi-Fi, and does absolutely nothing when the problem is power. A hub with no power has nothing to connect with. Only moving it to an unswitched supply fixes that one.
The short version
An offline alert on departure is normal and you can safely ignore it — once you have proved which kind it is. Do the key test and the disconnect test on the day you install the hub, and write down the answer. If you never did them, the backlog on the next arrival tells you anyway, for free.
The reason it matters is not the drive. It is the storage lot in November, when the disconnect goes off, the rig sits for five months, and the difference between a hub on the right circuit and a hub on the wrong one is the difference between a freeze alert and a spring surprise. Every device in the compatibility database is downstream of the hub still having power.
There is nothing to buy at the end of this one. The tire caps and the battery monitor both answer the question, but you buy those for the tires and for the battery, and they only settle this as a side effect. The fix here is a plug moved to a different outlet.
