The aim of this work is to assess the influence of different environmental attitudes and habit behaviours on ecological behavioural intentions affecting sustainability. A sample of Spanish citizens was asked to fill out a questionnaire expressing their intention with regard to an efficient behaviour (to adopt or reject a technological innovation for energy saving) and their environmental attitudes and behaviours. Behavioural intention was measured using a four-item scale expressing different levels of decision-making. Results show that habit behaviours related to sustainability are better predictors than environmental attitudes, and suggests that a sustainable future for humanity depends on changes in lifestyles.