The Prospero project explores the use of a conversational agent and investigates what is the most suitable occasion for delivering memory training. With the hypothesis that users are more likely to accept prompts for memory training during idle or relaxed moments (when they are not busy), we used physiological sensors to measure electrodermal activity (EDA) and heart-rate variability (HRV) to monitor the users' cognitive load and issued prompts when the cognitive load was low. Further studies are being conducted to test our hypothesis and evaluate the system.