In theory every room used for sensitive meetings needs a screening every time it is used. The only possible exception could be rooms that remain permanently locked except when used by a very select group of people. But a sophisticated screening to detect non-transmitting bugs may take several hours. Remember that most commercial breaches of security are created by staff themselves who agree to betray their own companies for money. And just in case you were still under the delusion that a swept room is secure, devices are available using lasers which allow someone to listen to a conversation taking place half a mile away using equipment operating at that distance .
Laser light reflects off window glass, carrying with it vibrations from noise inside the room.
Then there are the cameras. A high quality colour video camera operating in bright or dim light can now be squeezed into a screw head. The centre of a Phillips screw is more than large enough to contain the lens of such a camera, which can therefore be concealed in any light switch, or any area of any room where a Phillips screw head is visible. Networking means that every word spoken in one room in Australia can be heard in precise detail in any other country of the world day and night, using local telephone calls and Internet encryption. Most companies are still in the Stone Age when it comes to commercial security.