Explore a conference talk from CCS 2016 that introduces iLock, an innovative system for immediate and automatic locking of mobile devices to prevent data theft. Delve into the challenges of existing authentication methods and learn about the novel approach using active acoustic sensing for leaving detection. Discover the design goals, attacker models, and the implementation of Frequency Modulated Carrier Wave (FMCW)-based distance calculation. Examine user trace extraction techniques and the decision-making process for device locking. Analyze the system's performance in various scenarios, including one person leaving and landscape mode usage. Gain insights into the true positive rate, precision, and recall metrics when facing different types of attackers. Conclude with a power analysis of the iLock system and its potential impact on mobile device security.