A month ago we landed a payload reduction in the cloud bridge. This week we have a real number to put against it. Seven days of always-on cloud monitoring used about 100 MB of cellular data. That is roughly 14 MB a day, or 430 MB a month, on a system that never sleeps and never throttles when you stop driving.
What we measured
Headwaters has been live in the trailer since the beginning of April, publishing to the Farwatch cloud over a cellular hotspot. We started the week with 20.0 GB available on the plan and ended the week at 19.9 GB. That is the entire footprint of the system reporting in, with no other devices on that hotspot.
- 7 days used: ~100 MB
- Daily average: ~14.3 MB/day
- Monthly projection: ~430 MB/month
- Annual projection: ~5.2 GB/year
- Margin against a 20 GB plan: roughly 46x
The carrier reports usage in 0.1 GB steps, so the true weekly figure is somewhere between about 50 and 150 MB. A second week of data will tighten the band, but the order of magnitude is locked in.
Why "24/7" is the important part
Headwaters does not sleep. There is no ignition trigger, no motion gate, no parked-versus-driving mode. The system is live every minute of every day, and the publish cadence and payload do not change based on whether the rig is rolling or sitting in storage. That is the design, not a side effect.
That matters because the things you actually want a connected RV to tell you about happen when you are not there. A cabinet swinging open down the highway. A fridge door left ajar at the trailhead. A battery slowly drifting toward shutoff while the rig sits through a cold snap in storage. None of that gets caught by a system that wakes up only when you turn a key. It is caught by a system that is always listening.
Until this month, "always listening" had a different problem. It did not generate a bill, because hotspot plans do not bill overage. It just stopped reporting. Burn through the hotspot threshold and the carrier cuts data dead until the next billing cycle. The rig goes dark right when you most want to know what is happening. The fix was not to pay more, the fix was to stop spending the data in the first place.
One phone plan covers both jobs
Most folks already pay for a cellular hotspot or phone plan when they camp. Streaming, video calls back home, navigation, weather radar, ranger station check-ins. A 20 GB plan that is generous for a long weekend has 19.5 GB still on it after a month of 24/7 monitoring.
That is the headline. You do not need a second SIM, a second plan, or a separate "IoT" line for the rig. The same phone plan that keeps you connected at the campsite has all the headroom in the world to also run the trailer's nervous system.
The use cases people actually ask us about all sit comfortably inside that envelope:
- Storage mode. The rig is parked for weeks. You want to know if the door opens, if a battery dips, if cabinet sensors trip, if the temperature goes somewhere the plumbing does not like. The same hotspot that owners often disable to save data can stay on at well under a gigabyte a month.
- Pre-trip checks from the couch. Pre-cool the fridge, verify the leveling jacks are stowed, confirm the water heater is on. All of that runs over the same connection at a few kilobytes per command.
- Mid-trip peace of mind. You leave the trailer at the site and head into town. Air quality, tank levels, energy state, GPS, all still flowing into Farwatch on your phone. None of it eats your streaming budget.
- Boondocking. You finally found that perfect off-grid spot. Solar production, battery state, fresh and grey tank levels are still going up to the cloud, and you still have plenty of data left to actually enjoy the trip.
What changed in the cloud bridge
The earlier version of the cloud bridge was a simple per-topic rate limiter. Roughly 30 messages a second, distributed across all topics. It worked, but it cheerfully sent the same battery-percent value over and over because the topic was due for another publish.
The new bridge does three things instead:
- Change detection. Every outbound topic remembers the JSON it last sent. If the next message is byte-for-byte identical, the bridge stops there and does not transmit. Idle state stays free.
- Tiered intervals. Topics are grouped by how user-facing they are. Light and relay state forwards immediately on change. Energy and GPS sit in a 5 second tier with thresholds that bypass the gate when something actually moves. Air quality, tilt, and altitude sit in a 15 second tier. System diagnostics sit in a 30 second tier.
- 20 second heartbeat. Every 20 seconds the bridge republishes the latest cached value for every topic. That bounds maximum desync between the rig and the cloud at 20 seconds even if a packet was dropped, and it gives Farwatch a reliable liveness signal without needing per-topic timeouts.
For the energy and GPS tiers, "significant change" is defined in absolute numbers, not percentages: 0.5 V on battery voltage, 50 W on solar input, 2% on state of charge, charge type transitions, about 50 meters of GPS movement. Anything inside those bands stays quiet. Anything outside breaks through the interval gate immediately.
The result is a system that pushes a lot of bytes when something interesting is happening, and almost none when nothing is.
What this is not
This is not 14 MB a day because the system is asleep. It is 14 MB a day because the system is awake and disciplined about what is worth saying out loud. There is no power-state machine to break, no motion sensor to fail open, no firmware mode that has to flip when you turn the key. Park it, drive it, store it for a winter, the rate is the same.
It also is not a marketing number. The 100 MB came off the carrier dashboard for a real cellular hotspot connected to a real trailer running the real Headwaters image off main. The code is in cloud-bridge.js. Read it, change the tiers, run your own number.
What is next
We will let it run for another two or three weeks before calling the steady-state number final. We expect it to drift slightly with carrier rounding and reconnects in dead zones, not with anything the application is doing. If the trend holds, the recommended cellular setup for a TrailCurrent rig becomes the simplest possible thing: one phone plan, one router, both jobs.
It also sets the bar for everything else on the bus. The new Borealis safety sensor suite is about to add four more data streams (real CO2, VOC index, CO ppm, propane ratio, plus alarm flags). All of that goes up the same change-detected path, which means the additional cellular cost from a fully wired safety node will be measured in single-digit megabytes per month, not in plan upgrades.
Always-on monitoring used to be the line item that pushed people toward a dedicated cellular plan or pushed them away from cloud monitoring entirely. After this month it is a rounding error.