Earlier quoted context omitted.
Unless Heard has stopped working then this is not 100% true http://www.heardapp.com/ It may put a banner on the top bar but I've used this app and it worked just fine.
Very off-topic but what is your real-world use case for such an app? The site lists a couple but most of those seem to make more sense when using a recording app in the traditional, explicit, way (e.g. "we are having a meeting, I will record this meeting").
For myself I went the extra mile to just have my laptop record ALL audio but then felt this was a little too douchey/NSA-y and disabled the whole thing and wiped the audio. I wanted such a system not only for "You said this then and now you are saying that now" but to remember things I had said myself. I wanted to hook it up to STT to have a searchable archive of what I had said but again it was an invasion of privacy (to people around me) that I personally couldn't stomach.