Abstract: A shielding case is tightly mounted on a rim of a wheel having a tubeless tire thereon. A rocking rod extending from the case into the interior of the tire is supported at its substantially intermediate portion for pivotal movement from a neutral position, and a warning element for attracting the attention of a driver responds to the movements of the rod, when the tire is deflated due, for instance, to puncture. The warning element may either be one end of the rocking rod which strikes the case to give a series of sounds or an electromagnetic switch arrangement which energizes a buzzer.