What kind of tools and antennas are used? What is the method or technique to sweep a room for bugs?

 

Sweeping a room for bugs, is very difficult and involved,
basically you are trying to detect a signal,
simply, its a spectrum analyser and a water fall display

The hard bits are
a) getting the bug to transmit
b) finding the frequency / signal amongst the noise.

Getting the bug to transmit, look for "the thing" eagle in the us embassy,

finding the frequency
over radio, these things could easily use spread spectrum,
it would disappear into the noise,
the frequency band is unknown,
if your looking at 1Ghz and its transmitting at 5GHz your going to miss it

It could even be using its own cables, or the mains / phone line / computer cables as a parasite transmission.

There are also other bugs, that bounce light of an object. Could be a window, or through a window at another object, such as a picture. You'd never see it.

The great james bond frequency sweep thing is movie magic,

this site is a good read
https://www.cryptomuseum.com/covert/bugs/index.htm