Caution and common sense in using electronic surveillance and voice transmittal devices can help keep equipment and operations impenetrable. All material pertaining to electronic surveillance equipment should be marked "For Official Use Only" and should be treated with the same sensitivity as important criminal information. Recent court cases recognize the government's qualified privilege not to disclose sensitive investigative techniques. Initially, the court applied this privilege to the disclosure of observation posts used in visual surveillance. Federal courts have now extended this privilege to include the nature and location of electronic equipment. However, the issue of disclosure of technology to defense counsel and, ultimately, to defendants, is still a concern to government agencies.