  We present an optical wavefront shaping approach that allows tracking and
localization of signal hidden inside or behind a scattering medium. The method
combines traditional feedback based wavefront shaping together with a switch
function, controlled by two different signals. A simple, in transmission
imaging system is used with two detectors: one monitors the speckle signature
and the other tracks the fully hidden signal (e.g., fluorescent beads). The
algorithm initially finds the optimal incident wavefront to maximize light
transmission to generate a focus in the scattering medium. This modulation
process redirects the scattered input signal inducing instantaneous changes in
both monitored signals, which in turn locates the hidden objects. Once the
response from the hidden target becomes distinct, the algorithm switches to use
this signal as the feedback. We provide experimental demonstrations as a proof
of concept of our approach. Potential applications of our method include
extracting information from biological samples and developing non-invasive
diagnosis methods.
