Large-scale temperature monitoring: how to connect thousands of sensors without a cellular line per sensor
How to monitor the temperature of thousands of units with one connection per site, without modifying the equipment, with batteries that last years and without losing data.
For thousands of fixed sensors, the architecture that makes sense is short-range sensors that transmit to one gateway per site, not a cellular SIM per sensor. That way you pay for one connection per store or warehouse instead of one per unit, and the sensor batteries last for years. This is the Alephius architecture: Edge sensors over Bluetooth Low Energy (BLE) and gateways with WiFi or 4G.
The two possible architectures
| One cellular SIM per sensor | BLE sensors + one gateway per site | |
|---|---|---|
| Connections to pay for | One per sensor | One per gateway |
| Sensor battery | Shorter, because of the modem’s consumption | Years (up to 5 on Alephius Edge) |
| If the connection drops | Depends on each sensor’s memory | The gateway and the sensor keep the data |
| Best for | Mobile assets: trucks, containers | Fixed equipment: freezers, fridges, walk-ins, warehouses |
A concrete example: 100 stores with 20 refrigeration units each
Each unit gets an Alephius Edge sensor, so each store needs 20 sensors and 2 gateways, which cover the whole store. The full network looks like this:
| Cellular SIM per sensor | Alephius: Edge sensors + gateways | |
|---|---|---|
| Sensors | 2,000 | 2,000 |
| Gateways | Not applicable | 200 (2 per store) |
| Internet connections to pay for | 2,000 | 200 |
That is 200 connections instead of 2,000: 90% less spent on data plans, with the same monitoring on every unit. The exact number of gateways depends on each store’s floor area, walls and cold rooms, and it is defined in a site survey beforehand.
Installation: seconds per unit, no technicians
In a large rollout, what weighs most on cost and timelines is usually the installation, not the hardware. Multiplied by 5,000 units, every minute or every technician visit per unit turns into weeks of work.
There are two ways to connect a freezer, a fridge or a walk-in:
- Replace the unit’s controller with a connected one. It takes a refrigeration technician, cutting the power, opening the unit, and a controller that is compatible with that brand and model.
- Add a self-contained sensor. This is the Alephius way: the Edge sensor has its own battery and installs with industrial-grade 3M double-sided tape. Placing it takes seconds, with no tools, no power cut and no disconnecting the unit.
| Replacing the controller | Self-contained Alephius Edge sensor | |
|---|---|---|
| Who installs it | A refrigeration technician | On-site or project staff |
| Time per unit | A technician visit | Seconds |
| Power cut or opening the unit | Yes | No |
| Brands and models | Those compatible with that controller | Any |
| Supplier-owned units (for example, ice cream or beverage brand freezers) | Usually cannot be modified | Monitored all the same |
| If the unit is replaced | Has to be installed again | Remove it and install it on the new one |
To measure, log, alert and keep the history for audits, you do not need to modify the equipment.
A real case: 600 sensors across 30 stores in 5 business days
A supermarket chain connected 600 sensors across 30 stores in 5 business days: about 6 stores a day, with around 20 refrigeration units each. No power cuts, no units taken apart and no disruption to store operations. Replacing controllers, the same project would have needed one technician visit per unit.
Data continuity: three layers of backup
In a large rollout there is always some site without a connection or without power. What matters is that no readings are lost:
- Sensor: each Alephius Edge stores more than ten days of readings in its memory.
- Gateway: it holds what it receives while offline and sends it when the connection is back. During a power outage, it keeps running on its battery.
- Server: it confirms receipt of every data point and backs it up to disk before storing it, so a traffic spike or a database failure does not wipe out readings.
Three technical questions for the vendor
- How many connections will I pay for: one per sensor or one per site?
- How long does the sensor battery last inside a freezer, in real conditions?
- What happens to the readings if the internet or the power goes out over a weekend? Where are they stored in the meantime?
The full list, with costs, alerts, users and audits, is in the guide how to choose a temperature monitoring system.
How Alephius solves it
Alephius has clients running 1,000 sensors, connected 600 sensors across 30 stores in 5 business days, and its platform has been tested with tens of thousands. Its records have already been presented in laboratory audits. Alerts arrive on WhatsApp or by email through Alephius Assist, which notifies the person in charge, gives instructions, escalates to the next level if the deviation continues and records the resolution in a ticket.
See how it works in retail and cold chain and in logistics and warehouses.
Frequently asked questions
How many gateways do you need for 5,000 sensors?
It depends on each site’s floor area, walls and cold rooms, not on the number of sensors, and it is defined in a site survey beforehand. For example, a store with 20 sensors is covered by 2 gateways, meaning 2 connections instead of 20, ten times less spent on data plans than with a SIM card per sensor.
Why not put a cellular SIM in every sensor?
Because it multiplies the connectivity cost by the number of sensors, and a cellular modem drains far more battery than a Bluetooth sensor. For fixed sensors within the same site, a single connection shared through a gateway is cheaper and lasts longer.
Do you have to replace the controller or take the unit apart to monitor it?
No. The Alephius Edge sensor is self-contained, with its own battery, and installs in seconds with industrial-grade 3M double-sided tape, without cutting the power, taking the unit apart or calling a refrigeration technician. That is why it works with any brand, and also with units that belong to a supplier and cannot be modified.
What happens to the readings if the gateway loses its connection?
With Alephius, nothing is lost. The gateway stores what it receives and sends it when the connection is back, each sensor keeps more than ten days of readings in its memory, and the server backs up every data point to disk before storing it.