Previous studies have found that red giants (RGs) in close binary systems undergoing spin-orbit resonance exhibit an enhanced level of magnetic activity with respect to single RGs rotating at the same rate, from measurements of photometric variability, S ph ′ , and the chromospheric emission S -index, S Ca  II . Here, we consider a sample of 4465 RGs observed by the NASA Kepler mission, for which previous studies have measured S ph ′ and S Ca  II , in order to measure additional activity indicators that probe different heights in the chromosphere: the near-ultraviolet (NUV) excess from NASA GALEX photometric data, and chromospheric indices based on the depth of H α , Mg  I , and infared Ca  II absorption lines from LAMOST spectroscopic data. Firstly, as for Ca  II H&K, we observe that RGs belonging to close binaries in a state of spin-orbit resonance display larger chromospheric emission than the cohort of RGs, as is illustrated by an NUV excess and shallower H α and infrared Ca  II lines. We report no excess of Mg  I emission. This result reinforces previous claims that tidal locking leads to enhanced magnetic fields, and allows us to provide criteria to classify active RGs – single or binary – based on their rotation periods and magnetic activity indices. Secondly, we strikingly observe that the depths of the Mg  I and H α lines are anticorrelated and correlated, respectively, with the amplitude of solar-like oscillations for a given surface gravity, log g , regardless of the presence of photometric rotational modulation. Such a correlation opens up future possibilities of estimating the value of magnetic fields at the surface of RG stars, whether quiet or active, by combining spectroscopic and asteroseismic measurements with three-dimensional atmospheric models that include radiative transfer.