Cuffless sphygmomanometers may be useful alternative blood pressure monitors for screening and home healthcare. The main requirements for these devices are accuracy in the resting state, accuracy during dynamic blood pressure changes, and long-term stability. Intermittent measurements can ensure that the accuracy of active measurements mirrors that of measurements in the resting and dynamic states. This brief report proposes a new protocol to evaluate long-term stability based on a comparison with a medically approved cuff-based automated sphygmomanometer rather than an auscultatory sphygmomanometer. Dynamic changes in blood pressure are not usually assessed based on intermittent measurement with an over-the-counter (OTC) sphygmomanometer. Thus, validation testing focused on the accuracy of the OTC cuffless sphygmomanometer in the resting state and the long-term stability of the device, and the results were similar to those of the cuff-based sphygmomanometer. Further research and discussions are necessary to develop standards derived from high-quality evidence for manufacturers of OTC sphygmomanometers.