  Local unitary transforms cannot affect the quantum correlations between two
systems sharing an entangled state although they do influence the outcomes of
local measurements. By considering local squeezing operations we introduce an
extended family of observables allowing violation of the CHSH Bell inequality
for two-mode Gaussian systems. We show that local squeezing can enable or
enhance the identification of non-local two-mode states. In particular, we show
that local squeezing followed by photons/no-photons discrimination can suffice
to reveal non-locality in a broad ensemble of pure and mixed two-mode Gaussian
states.
