The inventors recently developed a system that authenticates and/or identifies a user of an electronic device based on passive factors, which do not require conscious user actions. During operation of the system, in response to a trigger event, the system collects sensor data from one or more sensors in the electronic device, wherein the sensor data includes movement-related sensor data caused by movement of the portable electronic device while the portable electronic device is in control of the user. Next, the system extracts a feature vector from the sensor data, and analyzes the feature vector to authenticate and/or identify the user. During this process, the feature vector is analyzed using a model trained with sensor data previously obtained from the portable electronic device while the user was in control of the portable electronic device.

In some embodiments, the movement-related sensor data includes accelerometer data gathered while the user is walking, wherein the accelerometer data reflects a characteristic gait of the user while walking.

In order to operate effectively, the system must carefully determine when to trigger collection of the sensor data. If the system collects sensor data too frequently, power is unnecessarily consumed during the collection process, which shortens battery life for the portable electronic device. Also, valuable network bandwidth can be wasted while transferring the sensor data to a server that analyzes the sensor data.

To address this problem, the disclosed embodiments provide a system that opportunistically triggers collection of sensor data while maintaining a low resource footprint.

In some embodiments, the trigger event comprises a silent push notification received by the portable electronic device.