An in-vivo sensing system for detecting blood comprising: an in-vivo sensing device comprising: i) a housing having: a capsule portion; a first portion enclosing a plurality of illumination sources, each illumination source configured to provide illumination at a different narrow band of wavelengths; and a second portion enclosing at least one light detector; wherein the first portion and the second portion define between them a gap configured to allow in-vivo fluids to freely flow into and out of the gap; and wherein the illumination sources and the at least one light detector face each other across the gap so that the light detector detects light that passes from the illumination sources through the in-vivo fluids in the gap at the different narrow bands of wavelengths; and ii) a transmitter for transmitting detected signals detected by the light detector; the system further comprising a receiver for receiving the detected signals; and a processing unit characterized in that the processing unit is configured for comparing the detected signals to a predetermined threshold at the different narrow bands of wavelengths thereby determining and distinguishing between the presence of bile and blood in-vivo. an in-vivo sensing device comprising: i) a housing having: a capsule portion; a first portion enclosing a plurality of illumination sources, each illumination source configured to provide illumination at a different narrow band of wavelengths; and a second portion enclosing at least one light detector; wherein the first portion and the second portion define between them a gap configured to allow in-vivo fluids to freely flow into and out of the gap; and wherein the illumination sources and the at least one light detector face each other across the gap so that the light detector detects light that passes from the illumination sources through the in-vivo fluids in the gap at the different narrow bands of wavelengths; and ii) a transmitter for transmitting detected signals detected by the light detector; i) a housing having: a capsule portion; a first portion enclosing a plurality of illumination sources, each illumination source configured to provide illumination at a different narrow band of wavelengths; and a second portion enclosing at least one light detector; wherein the first portion and the second portion define between them a gap configured to allow in-vivo fluids to freely flow into and out of the gap; and wherein the illumination sources and the at least one light detector face each other across the gap so that the light detector detects light that passes from the illumination sources through the in-vivo fluids in the gap at the different narrow bands of wavelengths; and a capsule portion; a first portion enclosing a plurality of illumination sources, each illumination source configured to provide illumination at a different narrow band of wavelengths; and a second portion enclosing at least one light detector; wherein the first portion and the second portion define between them a gap configured to allow in-vivo fluids to freely flow into and out of the gap; and wherein the illumination sources and the at least one light detector face each other across the gap so that the light detector detects light that passes from the illumination sources through the in-vivo fluids in the gap at the different narrow bands of wavelengths; and ii) a transmitter for transmitting detected signals detected by the light detector; the system further comprising a receiver for receiving the detected signals; and a processing unit characterized in that the processing unit is configured for comparing the detected signals to a predetermined threshold at the different narrow bands of wavelengths thereby determining and distinguishing between the presence of bile and blood in-vivo.