It is very dangerous to secretly record a conversation you are not a party to; in fact it is probably a felony!
The highest criminal court in Texas (equal to the Texas Supreme Court -- The Court of Criminal Appeals); held that it was a felony for a parent to get her child to sneak into a locker room and record the half-time speech. Now it must be noted that the child did not stay and in fact was not allowed to stay while the coach gave the speech. In other words, she was not a part to the speech or the recipient of the speech. In this case her mother, who took the recording and sent it to the school board was convicted of a felony. This case is very important because there Court did hold that it is OK to record someone even if your not part of the conversation if the the conversation takes place in a setting where the speakers don't have a "reasonable expectation of privacy". However the reasonable expectation of privacy is a moving target and while you might think they don't have a reasonable expectation of privacy, a jury and judge could differ. The best policy? Don't secretly intercept and record conversations between individuals. The Court in this case did affirm that under Texas and Federal law you can record someone without their consent as long as you are part of the conversation. The Court even said that you could secretly record your child and someone else because it is assumed that you can give consent for your child. But for me, I think that is risky behavior. In the employment context; if you secretly record a conversation that you are not a party to is very risky business. You could always argue that the speakers were in an office setting and had no expectation of privacy but Courts have held that there are some reasonable expectations of privacy in the work force. It is interesting to note that many employers specifically specify in their handbooks that you should have no expectation of privacy in the workplace; but I would hate to be indicted for a felony and have to depend on that defense. Long v. State, 535 S.W.3d 511 (Tex. Crim. App. 2017)