Rapid, accurate, and automated measurement of soil matric potential is desirable. Evidence suggested that the Watermark resistance block might be an appropriate and inexpensive tool, so we conducted an evaluation of its relevant characteristics. A number of these blocks were calibrated under laboratory conditions to determine their individual and aggregate responses to soil matric potential, soil type, and temperature. We found that the temperature response could be expressed as a single equation, valid for all tested blocks, but comparison against matric potential revealed that each block had a characteristic response. Furthermore, block responses were different in two soils and, for a given soil, not necessarily reproducible. Given these limitations, these sensors are probably useful only as relative indicators of soil water status.