Abstract: An activity monitor system monitors a location using a sensor system and detects and responds to “interesting events.” The system may detect events based on video processing of a substantially live sequence of images from a video camera. The system may use multi-region processing including modifying event detection based on motion in one or more regions, motion transitions, and/or motion entry and/or exit points. Events may be detected based on other sensors and the system may use a combination of sensor data to detect events. The system may store event data from the one or more sensors (e.g., video, audio, etc.) for interesting events and/or trigger alarm actions. Alarm actions may include sounding an audible alarm and enabling a substantially live video display on a monitoring device concurrently with the audible alarm. In embodiments, the activity monitor system is implemented using a smartphone and a wireless network camera.