Abstract: An alarm system operative in conjunction with a venocylsis set which includes a drop chamber coupled to the output of a fluid bottle. The alarm system is provided with a float disposed in the drop chamber and responsive to the level of fluid pool therein. A proximity switch sensitive to the float position is removably attached to the exterior of the drop chamber to produce a switching action when the fluid level falls below a predetermined value. An alarm circuit is coupled to the proximity switch to generate a warning signal when the switching action occurs.