When should you have your office swept for bugs?
Firstly consider whether someone really would be bugging your office. Is there information that a rival could use to their advantage? Are you being paranoid? Does it matter if you are being bugged?
Sadly, the old days of hearing buzzes and crackles on a phone line is no longer a good indicator of industrial espionage. Audio and video bugs are so small that only experts can find them in most cases. These bugs cost practically nothing and transmit what they record via mobile phone technology so the people who set a bug can listen in from anywhere in the world.
If you are concerned, go to a telephone that is outside the area of concern and call experts in bug sweeping to tell them about your concerns. They are trained in surveillance countermeasures and will be happy to help you resolve the problem.