inflationary scenario was proposed in the Starobinsky $f(R)=R+R^{2}/6M^{2}$ model [@Staro80]; improvement of the chaotic inflation through the non-minimal coupling $\zeta\Phi^2\,R$ of gravity and matter was proposed in [@FaUn88]; interesting example of the unified picture of the gravity and SM particle physics was given in [@Shapo08], where it was argued that the SM Higgs field $H$ strongly non-minimally coupled to gravity, $\zeta HH^{\dagger}R$, $\zeta\gg 1$, can give rise to inflation. (For a review of modified gravity in cosmology see e.g. [@CFPS2012]). Furthermore one expects that working ground–based gravitational wave detectors such as the Advanced Laser Interferometer Gravitational Observatory (Ad.LIGO) [@AdLIGO] or planned next generations Einstein Telescope (ET) [@ET] and space–based evolved Laser Interferometer Space Antenna (eLISA) [@eLISA] will give an unique opportunity to test GR and possibly to find some interesting observational challenges pointing to a new gravitational physics. In this respect it is quite important to know the signals at the detector to discern between competing theories.

In this paper we analyze the response of the gravitational wave interferometer to a gravitational wave signals that arise in scalar–tensor (ST) theories (see e.g. [@FM2003]). In those theories gravitational interactions are mediated by nonminimally coupled massless helicity $2$ field and a scalar 