It stands to reason that social unrest does not erupt out of the blue. Although there are a great many reasons why social dismay might descend into social disorder, only few yardsticks or indices can plausibly be used to gauge the potential for social unrest (PSU). If policy makers want to undertake public action to prevent social dismay escalating into social disruption, they obviously need to draw on practical sensors. This paper assesses critically the adequacy of two such measures, the polarization (P) index, and the total relative deprivation (TRD) index. The paper proposes a tentative guide to selecting between these two measures. A review of three stylized scenarios suggests that, where income redistributions reduce the number of distinct income groups, and when each group is characterized by a strong sense of within-group identity, the P index surpasses the TRD index as a basis for predicting PSU. When the within-group identification is weak, however, it is better to use the TRD index to predict PSU.