Abstract: Described herein is a device and system and method for the detection of naturally occurring gas bubbles in the bloodstream; in one embodiment, a wireless optical device may be placed on various parts of the body including a finger or earlobe or is coupled with the SCUBA mouthpiece and detects certain vital signs such as heart rate, blood oxygen saturation (SpO2) and respiration rate by analyzing the photoplethysmogram (PPG) from a miniature sensor. There is also a method and apparatus for real-time non-invasive optical monitoring of actual state of decompression sickness are presented. The method is based on simultaneous measurements of PPG signals in different locations of human body and analysis of such a factor as phase shifts between various locations, change the shape of PPG signal between different locations, existence and modification of slow trends and low frequency modulations and angular distributions of the out-coming light.