A wireless sensor device comprising: a flexible circuit board ; at least one sensor selected from the group consisting of a temperature sensor , a humidity sensor , an illuminance sensor , and other sensors that sense various environmental conditions; a controller that processes an output value received from the sensor; an antenna that wirelessly transmits a signal received from the controller ; a replaceable primary battery ; a first adhesive layer ; a flexible sheet ; a removable second adhesive layer between the flexible circuit board and the flexible sheet ; and a protective layer that protects the at least one sensor, the controller , the antenna , and the primary battery ; wherein the at least one sensor, the controller , the antenna , and the primary battery are on the flexible circuit board , wherein (a) the first adhesive layer , the flexible circuit board , and the flexible sheet are stacked together in this order, or (b) the first adhesive layer , the flexible sheet , and the flexible circuit board are stacked together in this order, wherein the at least one sensor, the controller , the antenna , and the primary battery are disposed between the flexible circuit board and the flexible sheet , wherein the flexible circuit board and the flexible sheet form a casing of the wireless sensor device , wherein the protective layer is disposed between the flexible circuit board and the second adhesive layer , and wherein the protective layer and the second adhesive layer are hollowed to form a space housing the primary battery . a flexible circuit board ; at least one sensor selected from the group consisting of a temperature sensor , a humidity sensor , an illuminance sensor , and other sensors that sense various environmental conditions; a controller that processes an output value received from the sensor; an antenna that wirelessly transmits a signal received from the controller ; a replaceable primary battery ; a first adhesive layer ; a flexible sheet ; a removable second adhesive layer between the flexible circuit board and the flexible sheet ; and a protective layer that protects the at least one sensor, the controller , the antenna , and the primary battery ; wherein the at least one sensor, the controller , the antenna , and the primary battery are on the flexible circuit board , wherein (a) the first adhesive layer , the flexible circuit board , and the flexible sheet are stacked together in this order, or (b) the first adhesive layer , the flexible sheet , and the flexible circuit board are stacked together in this order, (a) the first adhesive layer , the flexible circuit board , and the flexible sheet are stacked together in this order, or (b) the first adhesive layer , the flexible sheet , and the flexible circuit board are stacked together in this order, wherein the at least one sensor, the controller , the antenna , and the primary battery are disposed between the flexible circuit board and the flexible sheet , wherein the flexible circuit board and the flexible sheet form a casing of the wireless sensor device , wherein the protective layer is disposed between the flexible circuit board and the second adhesive layer , and wherein the protective layer and the second adhesive layer are hollowed to form a space housing the primary battery . <EOS>