R900 — the one with the leak flag
Neptune's water protocol, and the only message on the band that carries a field the meter has already interpreted for you.
R900 is Neptune Technology Group's water meter protocol. It is not part of the
Itron ERT family — separate lineage, separate design — but it lives
in the same band, behaves the same way from a receiver's point of view, and
rtlamr decodes it.
It is the most useful message on the band for a homeowner, and the reason is a single field.
Properties
| Property | Value |
|---|---|
| Band | 902–928 MHz |
| Commonly observed | ~915 MHz |
| Utilities | Water |
| Vendor | Neptune |
| Interval | Periodic; less frequent than gas ERTs |
| Payload | Cumulative consumption + leak flag |
| Encryption | None |
| Decoders | rtlamr |
rtlamr -msgtype=r900 -filterid=YOUR_METER_ID
The leak flag
Every other broadcast on this band hands you a raw number and leaves the analysis to you. R900 hands you a conclusion: the meter has been watching for continuous flow — water that never stops moving, across a window long enough that no plausible human use explains it — and it raises a flag when it sees it.
That pattern is a running toilet flapper, a slab leak, a dripping supply line inside a wall, or an irrigation valve that failed open. Caught in the week it starts rather than in the quarter's bill.
This is the strongest single argument for pointing a receiver at your water meter rather than your gas meter, even though water has the worse signal path and the longer interval. A gas reading tells you what you already knew from your bill. A leak flag tells you something you did not know and can act on today.
Two things to understand about how it behaves:
- It is a state, not an event. The flag reflects the meter's current assessment. It does not tell you when the condition started, and it will clear on its own once flow returns to a normal pattern.
- It is deliberately slow. The meter is looking for continuous flow over a long window precisely so that a long shower or a filling pool does not trip it. That means it will not catch a burst pipe faster than you will notice one — it catches the quiet leaks, which is the class that costs money for months undetected.
Confirming it is your meter
Water is the hardest case for this, and the ordinary advice — match the broadcast consumption to your physical register — is harder to follow when the register is at the bottom of a pit under a cast-iron lid.
The workable method: generate a known consumption. Note the broadcast reading, run an outside tap for a measured period, and watch which of the several IDs you are receiving moves. Yours is the one that responds. That test also incidentally verifies your decode pipeline end to end.
If nothing moves, work through only neighbours — on water, a strong neighbour and a silent own-meter is a common and explicable outcome, given that yours may be transmitting from inside a hole in the ground on the far side of your property line.
Next
Where this leads.