NOVELTY - The device (200) has a biometric sensor for sensing biometric parameters of a user. An accelerometer tracks activity of the user. A water-proof and dust-proof housing encloses a processor, a memory unit, an expandable display, a camera, a projector and a communication circuit. A band secures the device on a human body or under, within or on clothing, where the human body includes a wrist, an arm, a neck, a head, a leg, a waist, an ear, a finger and other parts of the human body. The band includes a rechargeable battery to provide power to the device.    USE - Wearable personal digital device i.e. mechanical hybrid smart watch (claimed).    ADVANTAGE - The display can be expanded by using a flip-up portion or detachable portion, bending the expandable display or attaching an additional display portion and unbending the display so as to provide a common enlarged display space such that the enlarged display space facilitates user interaction with the device by providing more space for displaying data in a convenient manner with enhanced user comfort. The band includes rechargeable batteries to power the device such that life time of the device can be increased. The device provides better habits-charts capabilities so as to enable the user to set goal regarding e.g. eating of healthy food, and view progress in goal achieving by registering events that comply with the goal set.    DETAILED DESCRIPTION - The activity of the user defines calories burned by the user, sleep quality of the user, breaths per minute of the user, snors breaks of the user, steps walked by the user and distance walked by the user. The access to the device is controlled by a password, a personal identification number (PIN) code and biometric authorization via fingerprint scanning, palm scanning, face scanning and retina scanning. The biometric sensor measures biometric parameters e.g. blood pressure, pulse, heart rate, glucose level, body temperature, environment temperature and arterial properties, of the user. The device is metal-banded, leather banded, plastic-banded or jewelry-banded, rimmed by jewelry and diamonds on a bezel, rimmed by jewelry and diamonds on an edge of the display. The device has an operating system e.g. Android (RTM: Linux-based operating system), iOS (RTM: mobile operating system), Firefox OS (RTM: Linux kernel-based open-source operating system) and wearable OS. The rechargeable battery includes a flexible battery, a set of button batteries, a curved battery, a stepped battery and a cable battery, where the flexible battery includes nanoparticles in semi-solid paste, a thin-film lithium-ion battery and a sodium ion battery with flexible molybdenum disulfide electrodes. The band is an expansion bracelet, one piece band and a two piece band. The expandable display is a touchscreen display e.g. flip up display, detachable display and bendable display. INDEPENDENT CLAIMS are also included for the following:    (1) an expandable standalone display    (2) a method for enlarging display space by utilizing a wearable personal digital device.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of an environment within which a wearable personal digital device and a method for enlarging display space using the wearable personal digital device are implemented.    Network (110)    GSM satellite (120)    Mobile base station (130)    External devices (140)    Wearable personal digital device (200)