Slate takes a look at privacy laws concerning the taping of conversations without the knowledge or consent or all parties:
Most states, as well as the District of Columbia, allow surreptitious recording of conversations—on the phone or in person—as long as one person involved gives permission, even if that person is you. Because the two men conducting the NPR sting were aware of their own recording, which took place in Washington, D.C., it was legal. (If no parties know about it, that’s wiretapping, which requires a warrant.)
What’s surprising is how many states, in this age of Flip cams and camera phones and surveillance cameras and helmet cams, have “two-party consent” laws. In 12 states—California, Connecticut, Florida, Illinois, Maryland, Massachusetts, Michigan, Montana, Nevada, New Hampshire, Pennsylvania, and Washington—all parties involved need to consent before one of them can record the conversation.
There are some exceptions to the two-party consent rules. In California, for example, you can record a conversation without the other person knowing if you believe it will collect evidence of a serious crime. […]
There are also exceptions to two-person consent when there’s no “reasonable expectation of privacy.” For example, a conversation at a legislative hearing could be recorded without informing all parties, since recording things is what people do in legislative hearings. Same with public speeches, shouting matches on the street, or any other scenario where you simply can’t expect privacy.
That still leaves some gray area. In your house, you can reasonably expect privacy. But what about conducting a loud conversation on your porch? If you don’t want to be recorded, a judge might say, go inside. Or say two people are chatting in low voices on a bench in a public park, with no one else around. On the one hand, they’re in a public park. On the other, if one interlocutor reasonably expects privacy since no one else is within earshot, the recording could be illegal. […]
You’d think the iPhone panopticon would make two-party consent laws look antiquated. Yet some states are enforcing them more vigorously than ever. In Illinois, for example, civil-liberties advocates are challenging a law that says you can be thrown in jail for 15 years for recording a conversation with a police officer. The penalty for recording a private citizen is up to three years in prison for a first-time offense, and up to five years for a second offense. Boston police, too, have arrested people for videotaping them in public areas.