A monitoring assembly for a pneumatic tire includes an electronic monitoring device having at least one sensor disposed in a protective body. The monitoring assembly is configured to float on a variety of liquids that are typically disposed within a tire. The protective body is liquid-tight and includes an encapsulation layer that encapsulates the substrate and sensors, a cushion, and a skin on the outside of the cushion. The protective body is substantially spherical allowing the assembly to roll about the inside of a tire without being permanently connected to the tire. The monitoring assembly is simply placed in a tire before the tire is mounted on a vehicle rim and allowed to move about loosely in the tire chamber when the tire is in use.