Abstract: This paper investigates networked fault detection in a finite frequency domain with an event-triggered communication scheme. Under the event-triggered communication scheme, the networked fault detection system is modelled as a two-mode switched linear system. The finite frequency input is defined on the basis of the time-domain interpretation of finite frequency inequality. By applying Finsler's lemma and the property of finite frequency input assembly, this co-design approach is proposed for fault observation and communication under high-frequency disturbance and low-frequency fault input. Finally, a numerical example is given to illustrate the effectiveness of the presented approach.