A device configured to provide an augmented reality, AR, service, the device comprising: a display; a camera; and a processor configured to: control the camera to obtain a surrounding image of surroundings of the device; control the display to display the obtained surrounding image; detect a plurality of real objects included in the obtained surrounding image; display a plurality of virtual icons mapped to the plurality of real objects detected in the surrounding image and indicating the plurality of detected real objects, overlapping the plurality of detected real objects, so that the user observes the plurality of real objects indicated by the plurality of virtual icons; recognize a plurality of real objects observed sequentially by eyes of a user wearing the device; and display the plurality of virtual icons representing the plurality of real objects gazed by the user sequentially on the surrounding image according to the order in which the user gazed at the plurality of real objects; determine whether the recognized plurality of real objects correspond to a plurality of objects preset as a password; based on determining that the recognized plurality of real objects correspond to the plurality of objects preset as the password, perform a preset task corresponding to the plurality of real objects and an order in which the plurality of real objects are observed. a display; a camera; and a processor configured to: control the camera to obtain a surrounding image of surroundings of the device; control the display to display the obtained surrounding image; detect a plurality of real objects included in the obtained surrounding image; display a plurality of virtual icons mapped to the plurality of real objects detected in the surrounding image and indicating the plurality of detected real objects, overlapping the plurality of detected real objects, so that the user observes the plurality of real objects indicated by the plurality of virtual icons; recognize a plurality of real objects observed sequentially by eyes of a user wearing the device; and display the plurality of virtual icons representing the plurality of real objects gazed by the user sequentially on the surrounding image according to the order in which the user gazed at the plurality of real objects; determine whether the recognized plurality of real objects correspond to a plurality of objects preset as a password; based on determining that the recognized plurality of real objects correspond to the plurality of objects preset as the password, perform a preset task corresponding to the plurality of real objects and an order in which the plurality of real objects are observed. control the camera to obtain a surrounding image of surroundings of the device; control the display to display the obtained surrounding image; detect a plurality of real objects included in the obtained surrounding image; display a plurality of virtual icons mapped to the plurality of real objects detected in the surrounding image and indicating the plurality of detected real objects, overlapping the plurality of detected real objects, so that the user observes the plurality of real objects indicated by the plurality of virtual icons; recognize a plurality of real objects observed sequentially by eyes of a user wearing the device; and display the plurality of virtual icons representing the plurality of real objects gazed by the user sequentially on the surrounding image according to the order in which the user gazed at the plurality of real objects; determine whether the recognized plurality of real objects correspond to a plurality of objects preset as a password; based on determining that the recognized plurality of real objects correspond to the plurality of objects preset as the password, perform a preset task corresponding to the plurality of real objects and an order in which the plurality of real objects are observed.