A data input device for use with a tracking surface having light-scattering properties. The device comprises a coherent light source for projecting a coherent light beam onto the tracking surface to reflect a speckle pattern. A detector having a field of view detects and images the speckle pattern. The detector operates in a tracking mode when the field of view intersects the coherent light beam. The intersection of the coherent light beam and the field of view comprise a detection zone. Relative movement between the coherent light beam and the tracking surface within the detection zone between is detected in the tracking mode, based on the reflected speckle pattern. Relative movement between the coherent light beam and the tracking surface outside the detection zone is not detected. A controller responsive to the detector operates in the tracking mode for correlating the imaged laser speckle pattern to track the relative movement within the detection zone.