  We propose a scheme for witnessing entanglement in phase space by
significantly inefficient detectors. The implementation of this scheme does not
require any additional process for correcting errors in contrast to previous
proposals. Moreover, it allows us to detect entanglement without full a priori
knowledge of the detection efficiency. It is shown that entanglement in single
photon entangled and two-mode squeezed states can be witnessed with detection
efficiency as low as 40%. Our approach enhances the possibility of witnessing
entanglement in various physical systems using current detection technologies.
