I like this idea, but hate the idea of needing a third party app. Something like this would have to be open for me to use it. I dislike the idea of a third part

I like this idea, but hate the idea of needing a third party app. Something like this would have to be open for me to use it. I dislike the idea of a third party writing the code that controls something embedded in my body. Not even for the typical reasons of 'ads and privacy'. What happens if the business fails? Someone pushes bad code? The organization is sold? Something we can't anticipate now? I'd need the certainty that I can take full control over it if needed.