Generally, all the DIY systems are similar hybrid closed loop systems. They’re designed to send temporary basal rate commands to the pump. They have hardware and software safety limits for insulin dosing, which you can adjust based on your preferences, and change those over time. You can set and adjust your regular targets in addition to setting temporary targets. If they break, or the controller battery dies, or it fails for any number of reasons, at the end of the temporary basal rate, they fall back to standard pump operation.