  We present the first system to determine fluid properties using the LiDAR
sensors present on modern smartphones. Traditional methods of measuring
properties like viscosity require expensive laboratory equipment or a
relatively large amount of fluid. In contrast, our smartphone-based method is
accessible, contactless and works with just a single drop of liquid. Our design
works by targeting a coherent LiDAR beam from the phone onto the liquid. Using
the phone's camera, we capture the characteristic laser speckle pattern that is
formed by the interference of light reflecting from light-scattering particles.
By correlating the fluctuations in speckle intensity over time, we can
characterize the Brownian motion within the liquid which is correlated with its
viscosity. The speckle pattern can be captured on a range of phone cameras and
does not require external magnifiers. Our results show that we can distinguish
between different fat contents as well as identify adulterated milk. Further,
algorithms can classify between ten different liquids using the smartphone
LiDAR speckle patterns. Finally, we conducted a clinical study with whole blood
samples across 30 patients showing that our approach can distinguish between
coagulated and uncoagulated blood using a single drop of blood.
