  The nature of black holes is one of most exciting issues in gravitational
physics. If there is an exotic compact object as the compact as a black hole
but without a horizon, gravitational wave echoes may be produced after the
merger. In this work, we show that for extreme-mass-ratio binaries, even during
the inspiraling phase of compact binary coalescence, the exists of hard surface
of the exotic compact object will produce detectable signals on the
gravitational waves. We predict that once the LIGO-Virgo-KAGRA, Einstein
Telescope or Cosmic Explorer detect such kind of sources, our model shows that
one can constrain the properties of surfaces of the compact objects in
inspiraling stage better than the current level.
