You check the thermostat twice before you lock the door. It says 72, the air conditioning is running, the blinds are down on the sunny side, and you still sit in the truck a moment before pulling away.
Anyone who travels with a dog knows that moment. Everything is fine when you leave, which is the only part of the afternoon you get to see for yourself, and the rest of it you spend estimating a number nobody is standing there to read.
Sun does most of the work
A parked vehicle in sun does not sit at the outside temperature. Light comes in through the glass, the interior absorbs it, and what radiates back off the dash and the upholstery does not get out again as easily. The inside climbs past ambient and keeps going.
On a mild afternoon in the seventies, a closed vehicle in sun can pass 100 degrees inside an hour, and most of that rise happens in the first thirty minutes. An RV is larger and better insulated than a car, which buys time rather than changing the direction of travel. A slide facing south with big windows behaves a lot like a greenhouse, and the shade you parked in at ten is somewhere else by two. None of that is on the forecast, and nothing outside the rig will tell you the number inside it.
Four ways a cool rig stops being cool
In almost every version of this story the air conditioning was on and working when the owner walked away, and then something upstream of it gave out.
- The campground breaker trips. Common on a hot afternoon with the whole loop running air conditioning, and it is a pedestal you cannot see from a trailhead.
- The park loses power. Nobody rings to tell you.
- The air conditioning cannot keep up. Running flat out and losing looks and sounds exactly like running properly. Only the temperature tells them apart.
- Somebody unplugs you. Rare, and it does happen.
From a trailhead all four look identical to each other, and identical to a perfectly ordinary afternoon on which nothing went wrong at all.
Silence, or one message
A temperature sensor and a shore power reading will not cool anything down. What they change is the guessing: the phone stays quiet, which means the rig is where you left it, or it buzzes once and you go back.
What it does not change: RoamVitals is a monitoring and convenience product. It is not a life-safety device. An alert depends on power, on an internet connection, and on a phone that has signal and is in your hand. Any of those can fail, and none of them are things we can promise on your behalf. Do not leave an animal somewhere that would become dangerous if the alert never arrived.
That is not fine print we would rather you skipped. It is why everything below is about margin and early warning rather than cutting it fine. A second pair of eyes is worth having. It is not the same as being there, and it is not a reason to take a risk you would not otherwise take.
Set it up so it earns its place
Floor level, not the thermostat
The thermostat lives high on an interior wall in the coolest part of the rig, which is not the part your dog is in. Put the sensor where the animal actually settles: floor level, living area, out of direct sun. It can read several degrees warmer down there than the wall claims.
Pick a threshold that lets you drive back
Set the number that gives you time to get back, not the one that describes an emergency. If the drive is forty minutes, an alert at 78 or 80 degrees is worth far more than one at 90, because at 90 the temperature is already climbing fast and you are still in the car.
A threshold that fires while everything is still fine is doing its job.
Shore power is the early warning
Temperature is the lagging indicator. By the time the rig has warmed enough to cross a line you set, whatever caused it happened a good while ago. Power loss is the leading one. Watch the shore power supply and you hear about the breaker when it trips, rather than twenty minutes later when the rig has warmed up enough to cross a threshold, and on a hot afternoon those twenty minutes are most of what you are buying.
Who is closer than you are?
An alert has to lead to somebody doing something, and the fastest somebody is usually not you. Campground staff can reset a pedestal breaker in minutes. So can the neighbour two sites down, if you have said hello and mentioned you might ring. Decide that before you go, not while standing in a car park reading an alert.
A note on the sensor itself
Any supported temperature sensor is fine here. You are asking whether the rig is at 76 or 96 degrees, not for a measurement defensible to a tenth, so an inexpensive broadcast sensor such as the Govee H5075 does the job. If that is where you are starting, the H5075 setup guide covers the pairing; if you already own a sensor, the compatibility database will say whether we can read it.
Whatever you use, put a battery alert on it. A sensor whose battery went flat last week is not reporting a problem, and neither is a rig that is perfectly cool, so from here the two look the same. A dead sensor is worse than no sensor, because no sensor at least keeps you honest about how little you know.
None of this makes that moment in the truck go away. It makes it shorter: the sensor is where the dog is, the threshold has the drive built into it, and the phone is face up where you will see it. Then you go and do what you drove there to do.
