The present invention relates to a noninvasive optical sensor having a reusable portion and a disposable portion and being capable of outputting a signal indicative of light attenuated by body tissue usable to determine one or more physiological characteristics of the body tissue, the optical sensor comprising a reusable component including at least one energy emitter and a detector capable of detecting energy attenuated by body tissue and capable of outputting a signal usable to determine one or more physiological characteristics of the body tissue, the at least one energy emitter being housed in one of a first casing and a second casing and the detector being housed in other of the first casing and the second casing, wherein the first and second casings are connected by a flexible connector and a disposable component including a first clip mechanically matable with the first casing and a second clip mechanically matable with the second casing, wherein the first clip includes a front stop such that the first casing is configured to mate with the first clip by vertically aligning a tip of the first casing and snapping the tip of the first casing below the front stop such that the first casing and first clip are substantially immobile when assembled together, and wherein the second clip and second casing mate in a vertically and horizontally open manner.
