Device for detecting characteristic signals of tissues and materials and methods for calculating thereof. Apparatus and methods for detecting the presence of tissue (skin) in pulse oximeter are disclosed. Specifically, analysis using optical techniques are used to identify characteristic signals of different compositions of matter. The present application discloses using a plurality of photodetectors at different distances from a source to measure light scattering through a variety of materials, and more specifically, to detect the presence of tissue.本發明提供用以偵測生物組織及材料之特性訊號之裝置及其計算方法。本發明提供之裝置及方法可偵測脈衝式血氧濃度計中是否存在有生物組織(皮膚)。尤其，本發明利用光學技術分析辨識不同物質組成之特性訊號。本發明利用複數與光源相隔不同距離之光檢測器以測量經由多種材料之光線散射，並藉此偵測生物組織之存在。
