  A unitary effective field model of the black hole evaporation is proposed to
satisfy almost the four postulates of the black hole complementarity (BHC). In
this model, we enlarge a black hole-scalar field system by adding an extra
radiation detector that couples with the scalar field. After performing a
partial trace over the scalar field space, we obtain an effective entanglement
between the black hole and the detector (or radiation in it). As the whole
system evolves, the S-matrix formula can be constructed formally step by step.
Without local quantum measurements, the paradoxes of the information loss and
AMPS's firewall can be resolved. However, the information can be lost due to
quantum decoherence, as long as some local measurement has been performed on
the detector to acquire the information of the radiation in it. But unlike
Hawking's completely thermal spectrum, some residual correlations can be found
in the radiations. All these considerations can be simplified in a qubit model
that provides a \emph{modified quantum teleportation} to transfer the
information via an EPR pairs.
