Abstract: An intravenous bag monitoring device is connected between an IV bag which holds fluid to be delivered to a patient and a hollow IV needle which is injected into a vein of a patient. The monitoring device comprises a chamber, an inlet leading to the chamber, and an outlet leading away from the chamber. A corrugated flexible wall panel is positioned in the chamber and divides the chamber into a first section which contains fluid and a second section which does not contain fluid. A spring is positioned in the second section of the chamber. The movement of the flexible wall panel in response to changes in hydrostatic force is resisted by the spring. An elongated push rod is attached to the flexible wall, passes through the second section and forms one of two contacts required to complete a warning circuit. The other contact is on the exterior of the second chamber.