bilderburg security question

for years the locations for bilderburg events have been known prior to their arrival. How can these douchebags be so sure the entire place isn't bugged? I was thinking anything transmitting a signal would be easy to find and remove, but remote recording devices in walls? If a person good at programming and construction knew what they were doing, could they not set a timer to turn on battery powered recording devices that transmit nothing, but hidden behind an expertly patched and color matched wall? How did the obama team go through the whitehouse and get rid of bugs? Beyond our paygrade I'm sure but it's an interesting thought. Love each other!