Methods, systems, apparatus, and computer programs, for tracking objects are disclosed. In one aspect, a method is disclosed that includes actions of obtaining an image, determining that a user of a first monitoring system has opted-in for object tracking by a second monitoring system that is remote from the first monitoring system, and based on a determination that the user of the first monitoring system has opted-in for object tracking: determining whether the obtained image satisfies a predetermined level of similarity to a stored tracking object image model stored on a first device of the first monitoring system, and based on a determination that the obtained image satisfies a predetermined level of similarity to the stored tracking object image model, generating a tracking update notification, and transmitting the tracking update notification to the second monitoring system that is remote from the first monitoring system.