Abstract: An apparatus for monitoring vital sign parameters in a biological entity is disclosed. In an embodiment, the apparatus includes at least one light source for transmitting light through the biological entity and at least one photodetector for receiving light transmitted through the biological entity. At least one light source and at least one photodetector are configured to be positioned proximate the biological entity in a manner that does not significantly impede blood flow through the biological entity. A signal is generated in response to the transmittance or reflectance of light through the biological entity. The signal corresponds to at least one characteristic of the generally unimpeded blood flow through the biological entity. The apparatus also includes a control system configured to analyze the signal to determine vital sign parameters in the biological entity. A method for monitoring vital sign parameters in a biological entity is also provided.