Accurate detection of scale inhibitors has always been crucial to scale control in industry. However, analyzing scale inhibitors at low concentrations, especially with polymeric scale inhibitors, remains an ongoing challenge. This paper presents an assay method designed to detect all types of scale inhibitors, especially at low concentrations, and an expert program developed to guide the method. The program guides the preparation of a field brine barite solution at a fixed barite super-saturation. Scale inhibitor concentration is then measured via the method of standard additions, assuming a linear relationship between the scale inhibitor concentration and the logarithm of barite induction time. Seven different scale inhibitors, including phosphonates, carboxylates and sulfonates, were detected in two typical synthetic brines at low concentrations. In addition, this assay method has also been applied to scale inhibitor detection in actual field brines. In general, this easily-implemented method can directly detect the residual level of any scale inhibitors in field brine about 0.1 mg/L active. Emphasis in this paper is on low concentrations. Measurement of low concentration scale inhibitors not only helps to monitor scaling tendency but also effectively prevents overuse of scale inhibitors and thereby protects the environment and saves money. This is one of the few methods that can detect most scale inhibitors at such low concentrations. Field applications, strengths, and interferences are discussed using laboratory and field examples.