1. A contaminant-detecting optical mouse comprising: a housing having a surface with an opening; an optics module contained within the housing and including: a substantially coherent light source or a non-coherent light source arranged to independently generate reflected light from an imaging surface external to the housing; at least one surface of the optics module exposed to the opening of the housing; at least one sensor configured to obtain a first image of the reflected light generated by the substantially coherent light source and a second image of the reflected light generated by the non-coherent light source; and a comparison module configured to evaluate differences between the first image and the second image for interference patterns that indicate a contaminant on the at least one exposed surface of the optics module; wherein when an interference pattern associated with contaminants in the first image is detected and a parameter of the interference pattern exceeds a threshold value, causing a containment to be identified, and when an interference pattern associated with contaminants in the second image is less than the threshold value, it is determined that a contaminant has been detected on the at least one exposed surface of the optics module.