A monitoring system sounds like a big technical thing. It is really just five parts: a sensor to measure, power to run it, a way to communicate the reading, somewhere to send it, and something to read it on. Once you can see those five parts, you can build one for the price of a few coffees — or buy one — and stop wondering what is happening when you are not in the room.
01The need.
You cannot be everywhere. You sleep, you run errands, you leave for the weekend — and that is exactly when the heater quits, the pump fails, the cooler drifts, or the power blinks. Monitoring is the plain answer to "what is happening while my back is turned." It is the most useful first system most growers build, because the first time it texts you at 2 a.m. it pays for itself.
02The five parts.
Every monitoring system, cheap or commercial, is the same five pieces. We have a plain-language lesson for each:
- Sense — the sensor that measures temperature, humidity, moisture, and the rest. Understanding Sensors.
- Power — wall current, battery, or solar to keep it running. Understanding Power.
- Communicate — Wi-Fi, a long-range radio, or cellular to carry the reading. Understanding Communications.
- Store — somewhere the reading lands and is kept. Understanding Data.
- Read — a dashboard or an alert so a human (or an AI) can act. Understanding Controls · Understanding AI.
You do not need all five to be fancy. A $12 sensor on Wi-Fi, sending to a free dashboard that texts you, is a complete, useful system. Appropriate technology says build the smallest one that solves your problem.
03How it works.
This stack is Collect·Have·Use, start to finish: the sensor and radio collect, the reading lands somewhere you have it, and a dashboard or alert lets you use it. The five parts above map straight onto the three steps — sense and power and communicate are how you collect, store is how you have, and read is how you use.
Most of OAT's hardware know-how lives here. We lean on the Home Assistant ecosystem and its standard way of describing sensors, so you ride on a huge open-source community rather than inventing your own.
04Collect — build the system.
| Buy a monitor | ~$40–200 | A ready-made temperature/humidity monitor that texts you. No wiring. The fastest way to the 2 a.m. alert. |
|---|---|---|
| Build it yourself | ~$12–60 | A small board, a sensor, and an afternoon. Cheaper, yours to repair, and it grows with you. The Build section has the sketches. |
| A hub and many sensors | ~$150–600 | A small home computer running Home Assistant, with sensors across several zones — one dashboard for the whole place. |
Go deeper
Hardware & Software · The Home Assistant section · the eight Fundamentals lessons · ESP32 sketches and push methods in the Build section.
05Have — keep the readings.
A monitor that only shows the current number is half a system. The other half is keeping the readings, so today's number has yesterday's and last winter's to sit next to. As data is king puts it, keep them and keep them yours — wherever they land, you should be able to pull them out and take them with you.
And a kept reading is only worth keeping if it's true. Before you trust a number — or act on it — make sure the sensor behind it isn't quietly lying: trust your gauge.
06Use — see it, get told.
- Act — an alert when a number crosses a line you set. The text that saves the crop.
- Make sense of it — a dashboard and history that turn a wall of numbers into "this room runs hot every afternoon" or "humidity spiked the night the mold started."
Those are the same readings used at two speeds — a fast loop that acts today and a slow loop that learns across seasons. The fast one needs tonight's number; the slow one needs all the ones you kept.
And once the readings are flowing and yours, every other stack on this site — Environment, Root Zone, Light — is just a different thing to point the same system at.
The shortest version
A monitoring system is five parts — sense, power, communicate, store, read. Build the smallest one that solves your problem (a $12 sensor that texts you counts), keep the readings and keep them yours, and use them to get told when something is wrong and to spot trouble early.
Frequently asked questions.
The honest version.
How do I monitor my greenhouse remotely?
Put a sensor (usually temperature and humidity to start) in the greenhouse, connect it to power and to a network — Wi-Fi if you have it, a long-range radio or cellular if you do not — and have it send readings to a dashboard or service you can open on your phone, with alerts when a number crosses a line. You can buy a ready-made monitor that does this, or build one with a small board and a sensor for around $12 to $30. The key parts are a reliable sensor, a way to carry the reading, and somewhere to see it and be alerted.
What is a farm or greenhouse monitoring system?
It is a setup that measures conditions (temperature, humidity, soil moisture, and so on) and makes them visible and actionable when you are not standing there. Every one, cheap or commercial, is the same five parts: a sensor to measure, power to run it, a way to communicate the reading, somewhere to store it, and a dashboard or alert to read it. The differences between an inexpensive build and a commercial system are scale and polish, not the basic shape.
Can I use Home Assistant for a greenhouse or farm?
Yes — it is one of the most popular foundations for grower-built monitoring. Home Assistant is free, open-source software that runs on a small computer, collects readings from inexpensive sensors, shows them on dashboards, and sends alerts or runs automations. Because it is widely used and community-supported, you ride on a large ecosystem instead of inventing your own, and the readings stay yours to keep and export. It scales from a single sensor to a whole multi-zone operation.
How do farm sensors connect to the internet?
Through one of three common paths: Wi-Fi (simple where you have coverage), a long-range radio like LoRa (which can reach a sensor a mile or more from the house with very little power, ideal for fields and outbuildings), or cellular (where there is no other network). The sensor sends its reading over that link to a hub or service that stores and displays it. The right choice depends on distance, power, and whether you already have a network where the sensor sits.
What do I need to build a sensor monitoring system?
At minimum: a small board (an inexpensive microcontroller), a sensor for what you want to measure, power, and a place to send the readings — often free software like Home Assistant or a simple endpoint. From there you add a way to be alerted. A basic build runs around $12 to $60 and an afternoon of setup. The Fundamentals lessons walk through each piece — power, communications, sensors — and the Build section provides ready-to-use sketches.
How much does a greenhouse monitoring system cost?
Anywhere from about $12 to thousands, depending on scale. A single build-it-yourself temperature/humidity sensor with alerts is roughly $12 to $30. A ready-made monitor is a moderate amount. A small-computer hub running Home Assistant with sensors across several zones runs a moderate amount. Commercial multi-zone systems tied into climate equipment cost much more. The good news: you can start at the low end and grow, because the readings are the same shape at every level.