A preset amount of weight change with respect to a load cell is monitored by a circuit which provides an alarm at an adjustable point prior to the weight change reaching the predetermined amount. A load cell and a phase detector circuit are driven by an oscillator which provides a pair of different phase signals. The phase detector is further provided with an output signal from the load cell indicative of the weight carried by the load cell and at the frequency and phase of one of the signals of the oscillator. The phase detector provides a direct current signal representative of weight carried on the load cell in response to its input alternating signals and the direct current signal is utilized for determining operation of an alarm device. An adjustable and switchable set point circuit is provided for developing an operating signal for the alarm device in response to the direct current signal from the phase detector, the switching function being effective to permit the direct current signal to approach a reference signal representative of the predetermined weight change unidirectionally regardless of whether the load cell is being loaded or unloaded.