  We propose two detuned Fabry-Perot cavities, each pumped through both the
mirrors, positioned in line as a toy model of the gravitational-wave (GW)
detector free from displacement noise of the test masses. It is demonstrated
that the noise of cavity mirrors can be completely excluded in a proper linear
combination of the cavities output signals. This model is illustrated by a
simplified round trip model (without Fabry-Perot cavities). We show that in
low-frequency region the obtained displacement-noise-free response signal is
stronger than the one of the interferometer recently proposed by S.Kawamura and
Y.Chen.
