Peace, quiet and an IoT SIM: upgrading the lab temperature monitoring system
13 May 2026
This post is a follow-up to an earlier piece on setting up temperature monitoring in the lab using Testo Saveris 2 data loggers. A brief recap is included below, but the earlier post has the full story.
The system that sas served us well
A few years ago, after considerable searching, we settled on a temperature monitoring solution for the lab freezers: Testo Saveris 2 data loggers, connected via WiFi to a cloud service that records temperatures continuously and raises alerts when critical limits are breached. The system covers three freezers across two rooms, has caught most real temperature excursion we have had, and has been running reliably for years.
The WiFi network the loggers connect to is not the university network – getting IT to cooperate with that particular request proved fruitless – but a dedicated personal hotspot running on a pay-as-you-go SIM from Three. The data loggers generate almost no data traffic, so this worked out to roughly £5 every two or three years. Simple, cheap, effective.
Or so it seemed.
The gradual accumulation of irritations
The setup had one persistent flaw. Our freezers are split across two rooms: two in a storage room, one in the lab. The router lived in the storage room – logical enough, since that is where the strain collection lives and where WiFi coverage mattered most. But the logger in the lab, further from the router, would occasionally fail to connect. Not catastrophically – it would pick up the connection again within an hour or two – but enough to generate a steady trickle of "connection failed" and "resuming normal function" emails. A minor irritation, nothing more.
The bigger irritations came later, and they came from Three.
First, Three changed their data policy. The days of purchasing a data package that rolled over indefinitely into the next month were over. Suddenly, I was buying a £5 – later £10 – data package every single month, for a system that was using almost none of it. Not a fortune, but deeply unnecessary.
Then came multi-factor authentication. Logging in to purchase that monthly data package now required entering a one-time code sent to the number associated with the SIM. Fair enough in principle. In practice, this meant logging into the router's interface via my phone to retrieve the SMS. Mildly annoying, but manageable.
Then the router's web interface stopped accepting login credentials. Most likely a JavaScript compatibility issue as browsers updated – though I am open to correction on the precise cause. Whatever the reason, I was effectively locked out of the D-Link DWR-932 router that had been quietly doing its job for years. The workaround? Every month: remove the SIM from the router, insert it into my phone, receive the authentication code, purchase the data package, remove the SIM from the phone, reinsert it into the router.
Every. Single. Month.
I contacted Three to ask for alternatives – a SIM with a different data structure, MFA via email rather than SMS, anything that might simplify the situation. Their response was consistent and magnificently unhelpful: had I considered switching to a plan with unlimited texts, unlimited UK calls, and several gigabytes of data?
Anyone who engages their brain for even one second will immediately grasp that unlimited texts and UK calls are of absolutely no relevance whatsoever to a temperature logger in a freezer room. But Three, bless them, remained convinced that more data was always the answer, regardless of the question.
AI to the rescue
This is where things improved considerably – and where AI deserves genuine credit.
© RudolphLAB, 2026
The more elegant solution, though, was the SIM. I described the problem to AI – low data volumes, long time horizons, no need for voice or SMS, just reliable connectivity for a handful of small devices – and the answer came back almost immediately: an IoT SIM.
IoT stands for Internet of Things, the catch-all term for the growing ecosystem of devices that connect to the internet without any human directly operating them. Smart meters, environmental sensors, connected equipment – and, as it turns out, laboratory temperature loggers. IoT SIMs are specifically designed for exactly this use case: low data consumption over extended periods, without the monthly package structure of conventional consumer SIMs. They are also not locked to a single network, registering instead with whatever network is available – a very useful bonus.
After a little research I found infiSIM. The deal: £15 for 500 MB of data, valid for five years or until the data runs out – whichever comes first – with a top-up option if needed. Delivery added another £15 for a courier, which stung slightly, but the arithmetic is hard to argue with. Roughly £30 upfront and perhaps a top-up sometime in the next five years, versus £10 a month and a monthly SIM-swapping ritual.
There was one small snag: getting the correct APN settings configured in the new router for the IoT SIM required navigating some menus that were not immediately obvious. AI walked me through the process step by step in plain language, the settings were entered, and the connection was established.
The current state of affairs
The system now looks like this: three Testo Saveris 2 data loggers, connected via a TP-Link TL-MR100 router running an infiSIM IoT SIM, feeding data to the Testo cloud service that monitors temperatures and raises alerts as needed.
The monthly SIM-swapping ritual is gone. The monthly data purchases are gone. The Three customer service conversations are, mercifully, also gone.
The connection issue with the more distant logger in the lab has not been entirely eliminated – the physical distance and intervening walls are what they are – but it occurs roughly ten times less frequently than before. The stronger router has made a substantial difference. The occasional connection dropout still happens, but it has gone from a regular minor irritation to a rare event that is easy to keep an eye on.
With a reasonable degree of optimism, this setup should now run without significant intervention for the next five years. For a system whose entire purpose is to sit quietly in the background and raise an alarm when something goes wrong, "running without significant intervention" is exactly the right outcome.
Sometimes the best technology is the kind you completely forget about.
Equipment mentioned in this post: Testo Saveris 2 data loggers, TP-Link TL-MR100 4G LTE Router, infiSIM IoT SIM.
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