A sensor assembly may include a housing made of a non-magnetic material. The housing may define an interior chamber. A shaft may extend from the housing. A bearing may be positioned around the shaft. An impeller may be positioned around the shaft and the bearing, and the impeller may include a magnetized portion. A sensor may be positioned within the interior chamber and/or proximate the magnetized portion. The sensor may detect the magnetized portion of the impeller to sense a rate of rotation of the impeller. The rate of rotation of the impeller may correspond to changes in flow rate of the fluid. As the flow rate of the fluid, and the rate of rotation of the impeller change in predetermined manners, control signals may be conveyed to activate a tool.