  How can we detect that our local, controllable quantum system is correlated
with some other inaccessible environmental system? The local detection method
developed in recent years allows to realize a dynamical witness for
correlations without requiring knowledge of or access to the environment that
is correlated with the local accessible quantum system. Here, we provide a
brief summary of the theoretical method and recent experimental studies with
single photons and trapped ions coupled to increasingly complex environments.
