  We study the FCNC $B_s \to \phi \gamma, \phi \nu \bar \nu$ and $\Lambda_b \to
\Lambda \gamma, \Lambda \nu \bar \nu$ transitions in the Standard Model and in
a scenario with a single Universal Extra Dimension. In particular, we focus on
the present knowledge of the hadronic uncertainties and on possible
improvements. We discuss how the measurements of these modes can be used to
constrain the new parameter involved in the extra dimensional scenario, the
radius $R$ of the extra dimension, completing the information available from
B-factories. The rates of these $b \to s$ induced decays are within the reach
of new experiments, such as LHCb.
