Without a substantial electronics background and some experience, you're unlikely, even with good gear to detect some of the variety of "devices" available. On the other hand, over the years, I've worked out a pretty good system for one of my clients. He arranges for a room, announces it to attendees, and then the morning of the meeting, changes rooms. Of course, I told him long ago that he had more to fear from folks on his own "team" than from an outside bugging job. Stay away from rooms with large outside windows, unless they are much higher than any nearby buildings.
....But then, it's usually cheaper and far less risky to "buy" info than to try to get it with a bug.