It's illegal but the evidence gathered is still admissible in a criminal case. https://ktla.com/news/local-news/its-illegal-to-secretly-record-conversations-in

It's illegal but the evidence gathered is still admissible in a criminal case. https://ktla.com/news/local-news/its-illegal-to-secretly-record-conversations-in-ca-but-the-audio-can-be-used-in-criminal-cases-state-supreme-court/ https://ktla.com/news/local-news/its-illegal-to-secretly-rec... I'm no aware of whether this applies in this circumstance (what is likely a civil case)