  We present the general scheme for construction of noiseless networks
detecting entanglement with the help of linear, hermiticity-preserving maps. We
show how to apply the method to detect entanglement of unknown state without
its prior reconstruction. In particular, we prove there always exists noiseless
network detecting entanglement with the help of positive, but not completely
positive maps. Then the generalization of the method to the case of
entanglement detection with arbitrary, not necessarily hermiticity-preserving,
linear contractions on product states is presented.
