Embodiments of the invention provide a system, apparatus and methods for measurement of biometric data of a diver. In many embodiments, the system includes a mouthpiece having a sensor device comprising a light emitter and detector configured to emit and detect light at a wavelength having an absorbance correlated with a level of a blood gas saturation e.g., oxygen, nitrogen, CO2. The emitter is positioned to emit light onto oral tissue of the diver and the detector positioned to detect light which is received from the oral tissue either by transmittance of light through the oral tissue or by reflection of light from the tissue. The target oral tissue can include one or both of gum or buccal tissue. Such embodiments allow data to be collected without having to wear additional sensors or measurement devices and allow for measurement of blood gas levels as the diver breaths through their mouthpiece.