  Absorption measurement is an exceptionally versatile tool for many
applications in science and engineering. For absorption measurements using
laser beams of light, the sensitivity is theoretically limited by the shot
noise due to the fundamental Poisson distribution of photon number in laser
radiation. In practice, the shot-noise limit can only be achieved when all
other sources of noise are eliminated. \textcolor{black}{Here, we use seeded
squeezed light to demonstrate that direct absorption measurement can be
performed with sensitivity beyond the shot-noise limit. We present a
practically realizable scheme, where intensity squeezed beams are generated by
a seeded four-wave mixing process in an atomic rubidium vapor cell. More than
1.2~dB quantum advantage for the measurement sensitivity is obtained at faint
absorption levels ($\leq 10\%$). We also present a detailed theoretical
analysis to show that the observed quantum advantage when corrected for optical
loss would be equivalent to 3~dB. Our experiment demonstrates a direct
sub-shot-noise measurement of absorption that requires neither homodyne/lock-in
nor logic coincidence detection schemes. It is therefore very applicable in
many circumstances where sub-shot-noise-level absorption measurements are
highly desirable.
