My question involves criminal law for the state of: California

I recorded my ex during a phone call we had (via cell phones). He did not threaten me or anything, as I know in that case it would have been legal for him to record me.

I know it is illegal to record phone calls in California unless there is consent by BOTH people, but I read something that says if there is a beep when I start recording, it is then legal.

My phone plays a beep whenever I start recording. It is a single beep.

Was me recording him legal? Would it be admissible into a court of law?