Power-efficient data collection by a personal imaging device regarding a user's interaction with an application on a mobile device by automatically switching on and off costly, power-consuming applications of the personal imaging device without the use of a radio signal. The personal imaging device detects a visual start signal displayed on the mobile device of a tagged application on the mobile device. The personal imaging device activates sensors of the personal imaging device for collecting data regarding the user's interaction with the application on the mobile device. The personal imaging device collects data regarding the user's interaction with the application on the mobile device via the activated sensors and stores the data in a repository. The personal imaging device detects a visual end signal displayed on the mobile device, ending data collection.