An attachable monitoring device includes a battery unit, a wiring board unit and a physical condition sensor and an adhesive. The battery unit includes a top surface, a bottom surface and a plurality of side surfaces connecting the top surface and the bottom surface. The wiring board unit covers the top surface, the bottom surface and one of the side surfaces and electrically connected to the battery unit. The wiring board unit includes a printed antenna printed on a first outer surface of the wiring board unit. The physical condition sensor is disposed on a second outer surface of the wiring board unit opposite to the first outer surface. The physical condition sensor includes a sensing region for contacting a user to detecting a physical-condition signal of the user. The adhesive is disposed on the wiring board unit for being attached to the user.
