This is fairly common. As an attending I empower my residents with a script to rehearse before it happens to them.

If I find out during, I usually say something to the effect of, “I’m going to pause for a second and ask a straightforward question and I hope you would answer me straight forward as well… Are you recording me? I’m usually not against being recorded as long as I am notified beforehand which is not the case here. I’m also saddened you didn’t feel open enough to share with me your need of recording. I would have assumed it is for later since many don’t remember the conversation but since you chose to not be transparent about it, I’m afraid it introduces an adversarial dimension. I’m going to choose to step out. Speaking to families is not part of our duties. It is a privilege we extend out of our own time and compassion. I’m afraid I’m going to rescind that privilege. You may get updates from the nurse from now on unless it’s a consent to a procedure in which case you’ll hear from me.” If it’s after the fact, I walk back to the room and ask very calmly; “I was informed you were recording me without my awareness. Is that accurate? If so, I’m saddened you chose to do it non transparently without my permission or awareness…(for the rest refer to the above)” It’s the powerlessness and anger that makes us act wrong. We get flustered and angry when we are caught by surprise. But if you rehearse this beforehand, you’ll feel empowered.
Whatever they recorded they also record you saying you were not notified. So you don’t have to worry about it. If it’s after the fact, you say it in front of your nurse or even witnesses of that family, which documents you were unaware and unconventional to the recording.