The laser wire scanner (LWS) is a non-destructive beam diagnostic which has been proposed for CLIC and other very low emittance electron beams. Measurements of the beam size can be made with submicron resolution. Different configurations for detecting scattered electrons are simulated using GEANT4, and the signals compared with the backgrounds resulting from expected halo losses. The requirements of the LWS are compared with conditions in the CLIC Beam Delivery System. Measurements of emittance with better than 10% accuracy seem achievable for realistic parameters
