Memento is a home-based reminder system that allows users to associate customized voice reminders with specific activities in their daily lives. Memento consists of three major components: (1) a handheld computing interface for initiating and receiving reminders; (2) a sensor subsystem that detects activity-related changes in the home environment; and (3) a central server that acquires sensor readings and attempts to infer user activity from the data in real time. These three components function together to provide a new and viable approach to augmenting human memory.