In a nutshell, there are 36 states that allow recording when only one party is aware of the recording process. This is called single party consent. There are 12 states where both parties must be informed of recording. In all states, placing a beep tone on the line should allow you to record without worry. In Illinois, for example, you must notify both parties by voice at the time of recording, or have a prior signed agreement that the recording may take place, or put a beep tone* on the line. To be practical, the information presented here may not be up to date or completely correct for your application. It is suggested you contact your legal staff regarding your specific recording application.

*A beep tone is a 1260 to 1540 Hertz tone, lasting .17 to .25 seconds, and broadcast for both sides to hear every 12 to 15 seconds during the recording process.

Additional information about recording your phone calls is available at the following web sites:

The Reporters Committee for Freedom of the Press has a very detailed site called Can We Tape.  It provides a practical guide to taping phone calls and in-person conversations in the 50 States and D.C. 

Professional Audio Laboratories has A Prosecutor’s Guide To The Use of Audio Taped Evidentiary Material.  This is a detailed overview of the basics involved in the use of audio taped evidentiary material from a prosecution point of view.

A great detail of information regarding forensic investigation of recorded audio is available at this board certified forensic investigator’s site, spyman.com.  His site has a number of references to state laws and links to interesting audio and legal sites.