  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 chromospheric emission S-index
$S_{Ca_{II}}$. Here, we consider a sample of 4465 RGs observed by the NASA
Kepler mission 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$\alpha$,
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 illustrated by an NUV excess and shallower H$\alpha$ 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 red giants --
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$\alpha$ lines are anti-correlated 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 including radiative transfer.
