In Study 1, the authors applied the prototype methodology to identify indicators that people use to predict whether a potential partner will "be there" for them at future times of stress. Using these indicators, the authors constructed a new type of measure of individual differences, the Knowledge of Indicators (KNOWI) Scale. It assesses knowledge of indicators that lead to an expectation that a partner will be there when needed. This measure applies signal detection methods to assess each participant's ability to discriminate good from poor indicators. Two studies showed that the KNOWI Scale predicts performance on two laboratory tasks. In Study 2, participants interacted with a confederate who described a problem revealing subtle cues that another person will not be there when needed. High-scoring participants on the KNOWI Scale recognized the cues more readily. In Study 3, participants read stories about spouses that portrayed a "secure base script." They then read stories about the interaction of inanimate objects and judged which story best matched the human story. High-scoring participants on the KNOWI Scale made more correct matches. In Study 4, the KNOWI Scale was shown to possess convergent and discriminant validity.