  Red giant asteroseismology can provide valuable information for studying the
Galaxy as demonstrated by space missions like CoRoT and Kepler. However,
previous observations have been limited to small data sets and fields-of-view.
The TESS mission provides far larger samples and, for the first time, the
opportunity to perform asteroseimic inference from full-frame images full-sky,
instead of narrow fields and pre-selected targets. Here, we seek to detect
oscillations in TESS data of the red giants in the Kepler field using the 4-yr
Kepler results as benchmark. Because we use 1-2 sectors of observation, our
results are representative of the typical scenario from TESS data. We detect
clear oscillations in ~3000 stars with another ~1000 borderline (low S/N)
cases. In comparison, best-case predictions suggests ~4500 detectable
oscillating giants. Of the clear detections, we measure Dnu in 570 stars,
meaning a ~20% Dnu yield (14% for one sector and 26% for two sectors). These
yields imply that typical (1-2 sector) TESS data will result in significant
detection biases. Hence, to boost the number of stars, one might need to use
only Numax as the seismic input for stellar property estimation. However, we
find little bias in the seismic measurements and typical scatter is about 5-6%
in Numax and 2-3% in Dnu. These values, coupled with typical uncertainties in
parallax, Teff, and [Fe/H] in a grid-based approach, would provide internal
uncertainties of 3% in inferred stellar radius, 6% in mass and 20% in age for
low-luminosity giant stars. Finally, we find red giant seismology is not
significantly affected by seismic signal confusion from blending for stars with
Tmag < 12.5.
