Two sensors sit on the dinette, same shop, same money, both with Bluetooth printed on the box. One turns up in the hub about forty seconds after the battery goes in, and the other never turns up at all.
The difference is not build quality or range, and it is nothing you could have caught by turning the packaging over in the aisle. It comes down to what each sensor does with a reading once it has taken one, and there are only a handful of possibilities worth knowing before you spend money.
Some sensors talk to the room, others talk to one device
Most of what we support broadcasts. Every few seconds it throws its current reading into the air, addressed to nobody, then goes quiet again. Anything in range can pick that up, your phone and our hub at the same time, and neither one gets in the other’s way. Nothing pairs, nothing is claimed, nothing has to take turns.
The other sort wants a connection. You open a session with the device, ask for a value, and it answers, and only one device can hold that session at a time. It is why a sensor you paired to your phone last spring quietly stops reporting to everything else, and why closing the manufacturer’s app can bring it back from the dead. In a rig where two or three things want the same reading, broadcast is simply less trouble, and most of our supported list is made of it.
Hearing it and understanding it are separate problems
Here is the awkward part of the dinette story. The silent sensor may well be broadcasting the whole time; the hub can see it advertising away quite happily and still do nothing useful with it, because the bytes have to mean something before there is a reading. There are three ways that goes wrong and we have hit all three.
Nobody published the layout
Plenty of manufacturers never document what their bytes mean, and nothing obliges them to. You can work it out by watching a device while you change the conditions around it, which is slow, and what it produces is a rule a firmware update can break without warning. Where we have done that work and confirmed it against real hardware, the device is listed as supported in the compatibility database. Where we have not, it is a candidate and says so, because a maybe dressed up as a yes costs somebody a return.
It is encrypted, and fairly so
Victron’s Instant Readout is the clearest case. Everything you want is right there, broadcast continuously and encrypted per device, so it becomes readable only once you paste that unit’s advertisement key into the hub. The key lives in VictronConnect, under Product Info, then Instant Readout Details, and it is a one-time copy and paste for each device. Worth doing rather than resenting: your state of charge is nobody else’s business in a crowded campground.
The firmware in the box will not cooperate
The Xiaomi LYWSD03MMC is the cheapest sensor worth owning, and out of the box it broadcasts encrypted MiBeacon that we cannot read. Reflash it with the ATC or pvvx custom firmware and it broadcasts openly instead. That is done from a web browser over Bluetooth and is well documented, but it is a real step you have to take before the sensor works with any hub, ours included. We list it as supported because it does work once flashed, and the firmware requirement is on its compatibility page rather than left for you to find after the four pack arrives.
Supported is a claim about today
The database is generated from the decoding rules the platform actually ships, so the word supported carries no optimism in it. A device is supported because the hub decodes it now, and a candidate because it does not, whatever we expect to add next month. If you are checking before you buy, search the model number printed on the box: every device has its own page listing what we read, how we read it, and each caveat that applies.
Nobody can buy their way onto that list. The status on every device page is produced by a build step that reads the catalog, and there is no field anywhere in that pipeline a commission rate could touch. When it says supported, that is the code talking rather than the shop.
When we can only read half of it
Some devices we read in part, and we would rather write that down than round it up. Victron’s battery monitors give us voltage, current, power and state of charge, which is everything most people ask of a shunt. Solar chargers and DC-DC converters from the same range are recognised on sight, but their record layouts are not decoded yet, so we do not claim them.
Mopeka’s Pro Check is the other honest half. It broadcasts a liquid level in millimetres, which becomes a percentage only once you have told the hub how tall the tank is. The Pro H2O sends the same frame, but sound travels through water differently than through propane and that curve has not shipped, so a water tank reports a raw level today rather than a calibrated depth. Neither is a reason to avoid the device; both are reasons to know which half you are buying.
Back to the two on the dinette
The silent one is almost certainly not broken. It is speaking a dialect nobody wrote down, or speaking it in code, or waiting for a connection your phone has been holding since March. The one that appeared in forty seconds did nothing clever: it broadcast in the open, in a documented format, to whoever happened to be listening. That is the whole difference between them, and it costs nothing to find out which you are buying while the box is still on the shelf.
