A bit of elaboration on the risks you could encounter here:
- CGM sensors can be faulty, depending on the rate of change of glucose (they’re actually not measuring blood directly, but interstitial fluids, which are generally lagging by about 15mins and can be inaccurate with large swings)
- battery dying out isn’t so bad, since the pump will just default back to its previous basal delivery settings
- there are safety maximums on insulin delivery, which prevent among other things, your typical overflow/precision errors
- maximums over time though is a more complex issue, something I haven’t yet dug into
And then there are... pump actuator failure, syringe seal failure (on syringe based pumps), valve failure (on valve based pumps), user error (on all systems), reservoir running out, occlusion, air bubbles and a thousand other things that can go wrong. This is not exactly easy material in the best of cases and most sensor packages do not have redundancy and will at best address only a small fraction of all possible failure modes.
Delivering something fast, accurate and under wildly changing conditions in the human body is far more complicated than most people assume.
I still remember when I had to be hooked up to an infusion pump for many hours at a time. In theory this was all pretty simple - I had a port (a permanent link to my blood system), the machine was hooked to the port, the machine was configured to deliver x ml per hour. Easy, right? Well ... moving my arm had a non-zero chance to trigger the alarm (alarm means "the machine has a problem to deliver the configured amount", please do something), moving in the bed had a higher chance, walking over the hospital corridor I could almost guarantee that at some point in a single walk (i.e. one length of the corridor) it would freak out and again start the alarm. And that's for a far easier system in very easy conditions. An insulin pump has to change what it delivers all the time and it has to work always. Sport, work, driving, running, ...
- CGM sensors can be faulty, depending on the rate of change of glucose (they’re actually not measuring blood directly, but interstitial fluids, which are generally lagging by about 15mins and can be inaccurate with large swings)
- battery dying out isn’t so bad, since the pump will just default back to its previous basal delivery settings - there are safety maximums on insulin delivery, which prevent among other things, your typical overflow/precision errors
- maximums over time though is a more complex issue, something I haven’t yet dug into