The first time my grill died mid-cook, it was mildly annoying. The second time, I had six people standing in the backyard and a tray of raw chicken. That was the day I decided a propane tank was a sensor waiting to happen. There is no good reason for a twenty-pound steel cylinder to be a black box in 2026, and there is certainly no reason to find out it is empty by the flame going out.
So I did what I do with every dumb appliance in this house eventually: I made it report to Home Assistant, locally, with no vendor cloud in the loop. This is the build log for monitoring propane tank level with a Mopeka Pro Check sensor and Home Assistant, reading the level straight off Bluetooth advertisements, and getting a low-tank alert while there is still time to swap or refill. It is the same local-first pattern I used for my fridge and freezer temperature monitor and my laundry-done notifications, pointed this time at a tank of flammable gas.
Why Not Just Use the Mopeka App
Let me be fair to the vendor first. Mopeka ships a perfectly usable Tank Check app. You pair the sensor, tell it your tank size, and it draws a nice gauge on your phone. If a manual glance at an app once in a while is all you want, you can stop reading and buy the sensor.
Here is why that was not enough for me. A propane alert is only useful if it is pushed, timely, and impossible to ignore. An app that I have to remember to open is not an alert, it is a diary. I do not want to think about the tank. I want the house to think about the tank and to interrupt me exactly once, when the level crosses a line, and never otherwise. That is an automation job, and automation lives in Home Assistant, not in a single-purpose phone app.
There is also the usual local-first argument. The app talks to the sensor over Bluetooth, but the account, the history, and any future features live on Mopeka’s terms. The reading I actually care about, the level of gas in my own tank, is a physical measurement I would rather own outright. The good news with Mopeka specifically is that you do not have to fight the cloud at all, because the sensor broadcasts openly and Home Assistant can just listen.
How the Mopeka Sensor Actually Works
The Mopeka Pro Check is a small puck that clamps to the bottom of a steel propane tank with three strong magnets. Inside is an ultrasonic transducer that fires a pulse straight up through the steel and the liquid propane, listens for the echo off the top surface of the liquid, and computes the depth. More liquid means a longer time-of-flight, and once you have told it the tank geometry, depth becomes a percentage.
The part that makes it perfect for local monitoring is how it reports. The sensor does not wait to be connected to. Several times a minute it emits a Bluetooth Low Energy advertisement, a tiny broadcast packet that anything in range can read without pairing or authentication. Packed into that packet are the raw reading, the tank temperature, and the sensor’s battery voltage. Home Assistant’s Mopeka integration knows how to decode that packet. So the entire data path is: propane surface, ultrasound, BLE broadcast, your Bluetooth adapter, Home Assistant. There is no phone, no app, no account, and no internet anywhere in that chain.
That is the whole trick, and it is why Mopeka is one of the friendliest devices in the smart-home world for people who refuse to depend on a cloud. The manufacturer did the local-first work for you by choosing an open broadcast instead of a locked-down connection.
Step 0: Figure Out Your Tank and Your Bluetooth Range First
Before you order anything, answer two questions, because they decide which sensor and whether you need an extra part.
What tank are you measuring? If it is a standard twenty-pound steel exchange cylinder under a grill or a patio heater, the plain steel-tank Mopeka Pro Check is exactly right, because it is tuned for the steel wall and the small diameter. If it is a large residential tank, an aluminum tank, or a poly tank, you want the Pro Check Universal instead, which handles those materials and bigger diameters. Buying the wrong one is the single most common mistake, so match the sensor to the tank material before anything else.
Can Home Assistant hear the tank? Propane tanks live outside, usually against an exterior wall, often behind a grill or down the side of the house. Bluetooth does not love walls. If your Home Assistant machine is a mini PC three feet from the grill, its built-in Bluetooth may hear the sensor directly. If your server is in a closet on the far side of the house, it will not, and you will need a Bluetooth proxy to bridge the gap.
The Bluetooth Proxy That Bridges the Gap
If Home Assistant cannot hear the tank directly, the cheapest fix in the entire hobby solves it: an ESP32 board flashed with ESPHome and configured as a Bluetooth proxy. For about five dollars, that little board sits near a window or in the garage, picks up the Mopeka broadcasts, and forwards them to Home Assistant over WiFi. To Home Assistant it looks exactly as though it grew a second Bluetooth antenna wherever you put the ESP32.
I already walked through the full Bluetooth proxy setup in my ESPHome Bluetooth proxy guide, so I will not repeat all of it here. The short version is that ESPHome has a one-line bluetooth_proxy: block, you flash it once, and from then on the ESP32 relays every BLE advertisement in its range, including the Mopeka’s. Place it on the inside of the wall nearest the tank and you are done. This is the same board and the same technique that also gives you room presence sensors and BLE thermometers, so it earns its slot several times over.
Mounting the Sensor and Getting the First Reading
Mounting is genuinely a thirty-second job. Wipe the bottom of the tank clean and dry, peel nothing, and let the three magnets on the sensor snap it flat against the center of the tank’s base. Center matters, because the ultrasound needs a clear vertical shot up through the liquid. Avoid the seam and the foot ring. That is the entire physical install.
On the Home Assistant side, if the sensor is in range of your adapter or your proxy, the Mopeka integration discovers it automatically. You will get a new device with sensors for tank level as a percentage, a reading quality indicator, the tank temperature, and the battery. You tell the integration your tank size and mounting so it can turn the raw echo into a real percentage. Within a minute or two you have a live propane gauge in Home Assistant that owes nothing to any server.
The reading-quality sensor is worth watching at first. A poor reading usually means the sensor is off-center, the tank base is dirty, or the tank is nearly empty. Once quality reads good and stable, trust the percentage as a trend.
The Automations That Actually Earn the Sensor
A number on a dashboard is not why you did this. The alerts are. Here is the small stack of automations I run, in the order they matter.
The low-tank warning. When the tank level crosses below thirty percent, Home Assistant sends a push notification to my phone: propane is getting low, order or swap soon. Thirty percent is deliberately early. It gives me a full weekend of buffer so a refill is a chore I schedule, not an emergency I react to. This one automation is the entire justification for the project, because it converts running out of gas from a surprise into a calendar item.
The critical-tank alert. A second automation fires a louder, repeating notification below ten percent, because at that point a grill session or a cold-snap furnace run really can empty it. I make this one persistent so it nags until acknowledged.
The refill detector. When the level jumps up by a large amount in a short window, Home Assistant knows the tank was swapped or filled and logs the date. Over a year this quietly builds a real consumption history, so I can see how much propane the winter actually cost and when I typically refill. No spreadsheet, no guessing.
The sensor-battery guard. Because the sensor reports its own battery, one more automation warns me when that battery drops below twenty percent. This closes the loop so the watcher never dies silently. A monitoring system that can fail quietly is worse than none, because it teaches you to trust a number that stopped being true.
I keep the alert thresholds as input_number helpers rather than hard-coding them, so I can nudge the low-tank line without editing YAML. If you cook a lot in summer, raise it.
What It Cost and What It Replaced
The sensor is roughly twenty to thirty dollars, and if you need a proxy, add five for an ESP32. Call it thirty-five dollars all in for a grill tank. Against that, weigh one ruined cookout with guests standing around, or one furnace that quit on the coldest night because the tank ran dry while nobody was looking. The sensor pays for itself the first time it saves you from either.
It also replaced a habit I did not enjoy: the periodic lift-and-heft of the tank to guess how full it was, which is both unreliable and mildly ridiculous. Physics does the guessing now, and it tells my phone.
The Bottom Line
Propane is one of those systems that stays invisible until it fails at the worst possible moment, and that is exactly the profile of a thing worth instrumenting. The Mopeka sensor makes it almost too easy, because it broadcasts openly over Bluetooth and Home Assistant reads it directly, so you get full local monitoring with zero cloud, zero account, and about a minute of setup once the sensor is on the tank.
If you run a grill, a patio heater, or a residential propane system, buy the Mopeka Pro Check for a steel exchange tank or the Pro Check Universal for a larger or non-steel tank, add a cheap ESP32 as a proxy if your server is out of range, and wire up the low-tank alert. It is a thirty-minute build that quietly removes an entire category of annoyance from your life, and it does it without asking you to trust anyone’s cloud with the level of gas in your own tank. That is my favorite kind of automation: small, local, and the sort of thing you forget about precisely because it never lets you down.