They did.... and the vibrations let them listen in. But nobody was burned.
It depends on the power level.Mere milliwatts could suffice for the remote listening,and be less likely to be detected.
Increase the power level to a thousand watts and effects will happen.
Early radar techs develpoed eye issues just as early X-ray users developed cancers. Unseen dangers take longer to be recognized.
Not that there couldn’t have been pepper spray or something else deliberately contaminating the seating.