Abstract: A device for the reliable detection of air or air bubbles in transparent or translucent tubing carrying a fluid which includes a transmitter element for transmitting a light beam to the fluid contained in a large-bore thin-walled transparent tubing, and a pair of first and second light receiver devices for receiving reflected and transmitted light emitted from the transmitter element and which is incident upon the fluid conducting tubing. The light transmitter and receivers are located within a body member around the fluid conducting tubing. Also, an acrylic optical spacer which has a passage for accommodating the tubing is located within the body member. One light receiver is disposed at a 90.degree. angle in relation to the optical axis of the transmitter, while the other receiver is arranged at a 180.degree. angle. Outputs of the light receivers are applied to a processor, which processes the light receivers outputs to detect air in the tubing.