For tips on sweeping a room for surreptitious surveillance devices, look no further than the Federal Bureau of Investigation. That's where members of the federal government have been going for years to find out who's wiretapped their telephone or implanted a microphone in their corner office. And now we know a lot more about the bureau's routine wiretap inspections thanks to GovernmentAttic.org, a website that publishes documents from Freedom of Information Act requests. The site has published a 66MB cache of correspondence from 1952 to 1995 detailing various issues of telephone security often involving paranoid government officials from senators to post master generals to secretaries of the Department of Agriculture to President Richard Nixon who think someone is surreptitiously listening to their conversations. 

It's going to take an army of readers to rummage through the entire cache of FBI documents but from what we've read so far, much of the correspondence involves government officials requesting wiretap inspections from the FBI, typically because they fear sensitive information has leaked from their office, and, upon inspection, the FBI finds nothing. Interestingly, they do often provide an informative report on how they went about sweeping the room.

As you can imagine, the descriptions of wiretap sweeps get much more technical from the '50s to the '70s to the '90s. In the old days, a wiretap inspection was simpler. Take this sweep of the office of Postmaster General Arthur Summerfield in 1953. 

Thank God the walnut paneling wasn't jeopardized!

But at least we know where to check. (Who would've thought to inspect the fireplace?) Another memo from 1953 between a government official and the FBI offers other areas to watch out for, including electrical outlets, the walls for concealed microphones, any radio-transmitters in the room,  tele-mike installations and the door jamb—never forget to check the door jamb! In another memo a few years later, the inspectors go all out, replacing the old wire from a wire duct to "prevent its use as a microphone cable." 

As the years go by, the FBI gets less descriptive about how they inspect an individual room for bugs, merely saying that they "checked" it. Take this memo from 1985:

Still, some of the later memos give a sense of what modern devices in a room could present a threat (i.e. would be easy to implant a recording device into). Like in this memo from 1984 about the vulnerabilities at a training classroom of the FBI. Here's what they say to look out for:

Unfortunately, as the FBI warnings from the '80s through the '90s emphasize, even checking all of these items can't offer 100% protection (and when it comes to cell phones and smart phones—that's another story).