A door is a moment. Water is an afternoon.

You get back to the storage lot in March and the generator cover is gone from the bay. There is a sensor on that bay door. Its history is a flat line: closed, closed, closed, all winter. Nothing opened, according to the only thing that was watching.

The sensor did not fail. It was asked to catch a moment, and a moment is the one thing a polled reading can miss. A door contact reports every 60 seconds at best and every 120 on the generic rule — so a bay can be opened, emptied and shut again inside a single interval, and the record will honestly show nothing at all.

What a person cannot do is put back the water they used, the propane they burned, or the electricity they drew. Those readings accumulate, and an accumulating reading cannot be missed by polling late. That is the whole of this article, and it is the half the door and motion guide does not cover.

Why the instant is the weak reading

Three limits stack on any event sensor, and none of them is a fault.

Resolution. A BTHome door or motion sensor reports every 60 seconds. The hub’s fallback rules are slower still — 120 seconds for a plain door contact, 90 for motion. Anything shorter than that window is invisible.

Quiet hours. A bay opening is not a safety alarm, and only safety alarms escape quiet hours, so one at two in the morning waits until they end. You are told at breakfast about something that happened in the dark, which is a record rather than a warning — and it is worth deciding in advance whether that is acceptable, because there is no per-rule exception to buy.

Rule shape. There is no “open for longer than” rule: a rule fires when a reading crosses a line, so any poll that sees a door open raises it. That makes a door contact an away-mode sensor, switched on when you leave and muted when you are living in the rig, or it reports every trip to the fridge. There is no way to say “three motion events in five minutes” either, which is why pointing a motion sensor at a doorway is a placement fix for a problem the rules cannot solve.

The traces that accumulate

a. The gray tank, which only goes one way

This is the strongest reading in the article and almost nobody sets it. Water used has to go somewhere: the fresh tank falls and the gray tank rises, both by roughly the same amount, and neither number goes back. A SeeLevel board reads every 120 seconds, but the interval hardly matters — the evidence sits there until you dump it.

Set a warning just above wherever you left the gray tank. On a rig you have closed up for the winter that alert has exactly one meaning, and it is not a plumbing meaning. Reading tank levels covers the rest of what those numbers do.

b. Propane, against the cabin temperature

Propane going down while nobody should be aboard is heat or cooking that somebody asked for. A Mopeka reads every 300 seconds — the slowest interval in the catalog and completely adequate for something that empties over hours.

The pairing is what makes it readable. Propane falling with the cabin warming is a furnace somebody turned on. Propane falling with the cabin cold is a fridge running on gas, which is probably you having left it that way in October. Neither number alone separates those.

c. A load appearing on shore power

If the rig is plugged in, a Power Watchdog is the fastest reading available anywhere in this article at 30 seconds. Draw appearing on a rig that should be drawing nothing but its converter trickle is somebody using it. Learn the idle number first, because a fridge on AC, a tank heater pad and a converter topping up a bank all raise it for ordinary reasons — winter check-ins covers learning that baseline.

The cord going dead is the other half: on a stored rig that is the pedestal, the park, or somebody unplugging you.

d. The roof air being started

A Micro-Air EasyStart counts lifetime starts, and a start count that moved while the rig was shut up is a person, not a thermostat doing its job — a thermostat cycling shows as the cabin temperature falling alongside. That decode came from the community and has not been on our bench, and the module answers only while the air conditioner has power, so its silence means nothing.

e. A tag that counts being handled

A RuuviTag is the only device in the catalog that counts its own movements, so one stuck to something you would hate to lose records that the thing was picked up. It reads every 60 seconds.

Did the rig move?

Nothing we read reports position, orientation, tilt or location. There is no GPS in the catalog, no accelerometer beyond that movement counter, and no leveling system decoded. So this question is inference or it is nothing, and the honest inference is the tires.

TPMS caps warm as wheels turn and their pressure climbs with them, all four together, which nothing stationary does. Combine that with a gap in the hub’s history — the rig left the Wi-Fi it was parked on — and you have the closest thing available to “it went somewhere”. The catch is the same as always: our rule matches caps advertising under a name beginning TPMS, so caps sold under another name are never read and their silence proves nothing.

One thing not to reach for: Lippert’s TireLinc broadcasts a presence beacon and nothing else today, and CO2 is not an occupancy sensor here either — the Aranet4 is detected rather than decoded, and it only broadcasts at all once its own app’s integrations are switched on.

The combinations

An instant and an accumulation, read together, which is the cookbook pattern doing the most work it does anywhere.

• A bay door opened, and a tag inside that bay moved in the same minute — somebody reached in. The door alone cannot separate a hand from a latch that shook loose on a rough road.
• Gray rising and fresh falling by about the same amount, with nobody aboard — somebody used water. This is the pairing that cannot be missed between polls.
• Propane falling and the cabin warming — heat somebody asked for. Falling with the cabin cold is the fridge on gas.
• A door event, and shore power draw appearing a minute or two later — inside and using the rig, rather than a door that moved.
• Start count moved and the cabin temperature was already comfortable — a person started the air conditioner. A thermostat would have been chasing a rising number.
• All four tires warming and climbing together, with a gap in the history — the rig went somewhere. No single tire doing it is a tire problem, not a movement one.
• A door reading closed all winter and something missing anyway — the event fell between two polls. That is not a fault, and it is why the readings above exist.

What none of this tells you

Who, or what they did. Every reading here says a person acted on the rig; not one of them says anything about the person. There is no camera, no recording, no identity, and nothing that reaches anybody on your behalf.

What to do about it

If the rig is stored and you own a SeeLevel board already, set the gray tank warning just above where you left it and you are done. That single alert is free, unmissable, and answers the question better than a door sensor does.

Add the door contact as the fast half of a pair rather than as the answer on its own, and turn it on only when you leave. Then read both together: the door tells you when, and the tank tells you whether anything actually happened.

Where to get one

Most of this is readings you already own, set to different thresholds. The one purchase genuinely aimed at this page is a tag for the thing you would least like to lose. The compatibility database has the rest, and the door and motion guide is the argument about contacts themselves.