Habits play a central role in shaping everyday behaviour, supporting both health-promoting and maladaptive patterns that are difficult to change. Habits are typically defined as cue-response associations that automatically trigger behaviour when familiar contexts are encountered. However, accounts differ in how cues translate into action: do they directly trigger behaviour, or do they create a preparatory state that makes action more likely? This review advances and evaluates the concept of the habit impulse – a cue-triggered event in the preparatory stage preceding behaviour, reflecting readiness to perform a learned action that may or may not be enacted. Drawing on associative learning and computational perspectives, we show that adding this intermediate stage helps separate response preparation from behaviour and its regulation. We synthesise evidence from behavioural tasks, self-report measures, reaction time paradigms, and neural methods to assess whether this preparatory stage can be detected. Although response preparation and behaviour can sometimes be separated, most existing measures of habit capture outcomes rather than the preparatory stage itself. Current evidence therefore cannot determine whether, or to what extent, the habit impulse is observable, as null findings may reflect either its absence or limitations in measurement. Methods for directly capturing the preparatory stage preceding behavioural enactment (or inhibition) is essential so that the habit impulse can be properly operationalized and, in turn, used to advance theory, improve measurement, and optimize behaviour change interventions.