Abstract: Spectroscopic devices and techniques for determining the presence or absence of an analyte of interest or the presence or absence of desired characteristics of an object are provided. In an embodiment, a portable device or attachment for a smart phone or comparable device includes a light source and a detector. The detector detects light after reflection from a target surface and, based upon attributes in the detected light absent from the emitted light such as covariances among different wavelengths, determines the presence or absence of the analyte of interest.