Abstract: A warning device for checking if an ostomy, drainage, or wound bag is full and needs to be emptied or if an IV bag dispensing medication or blood is empty and needs to be replaced. The warning device incorporates a unique sensor that adapts to the shape of the filled bag. The sensor can be easily attached to the outside of bags currently in commercial production or optionally integrated by a manufacturer onto a bag and the sensor does not require any additional countervailing force or external reference surface. An electronic module attached to the sensor can be programmed to produce a warning signal when an ostomy or drainage bag is full or when a bag dispensing medication or blood is below a predetermined level or is almost empty.