In some embodiments, the trigger event comprises a notification received by the portable electronic device from a wireless beacon.

In some embodiments, the trigger event comprises a periodic notification, which is sent at a predefined interval.

In some embodiments, the trigger event comprises an adaptive notification, which is sent at a variable interval determined based on feedback generated by a learner, which processes the collected sensor data. This feedback can relate to one or more of the following: a change in confidence level for the identity of the user; a battery level for the portable electronic device; a usage pattern for the portable electronic device; and a received notification associated with the portable electronic device.

In some embodiments, the trigger event comprises a detected activity of the user determined from the collected sensor data.

In some embodiments, the trigger event comprises a notification that the portable electronic device has entered or exited a predefined region associated with a geofence.

In some embodiments, the trigger event comprises one or more of the following: a change in lighting; a change in sound; a change in magnetic field; a detected keyword; a detected near-field communication (NFC) signal; a received message notification; a received telephone call; a user-interaction event associated with the portable electronic device; an interaction event between the portable electronic device and an external device/sensor; a screen-on event; a screen-off event; a device-unlock event; a device-unlock failure; an application-opening event; a switching-to-an-application event; a switching-cell-towers event; an install-application event; an uninstall-application event; a change in a device setting; a screen brightness adjustment; and a photograph-taking event.