Abstract: The present invention is directed to a wheel condition detection and signalling device. The device includes a chamber which is capable of being attached to a wheel of a truck to rotate therewith and a pendulum having significant mass and is rotatably mounted within the chamber in such a manner that the pendulum remains generally non-rotating during rotation of the chamber. The device also includes a detector means for detecting an unacceptable condition of the wheel and emitting a signal dependent upon such condition and a transmitter for transmitting that signal to a receiver. The chamber carries a wire coil which is mounted on a core having two outside parallel arms provided with end faces.