Actually, they don’t even need hidden microphones if you’re speaking in a room with windows.
The FBI has a laser listening device that they focus on the glass. It coverts the sound vibrations of the glass to a wave, which reflects back to the “transceiver”.
Found out about it over a decade ago, when they busted a guy here for bank/wire/internet fraud.
Probably many agencies have them now.
Remember when Sec. of State George Shultz had to use a magic slate writing pad to thwart espionage?