A system is provided for indicating excessive wear of brake linings. The system is usable on vehicles such as automobiles, cars, trucks and busses as well as aircraft or other applications where it is desirable to detect excessive wear of brake linings during operation thereof. The system includes an acoustical signal generating device having an air inlet normally closed by the brake lining. When the lining wears away to a minimum safe thickness, the inlet is opened and ambient air flows into the generator to produce an acoustical signal. An acoustical receiver is positioned in spaced operative relation to the brake system and responds to the acoustical signal to provide a warning indication on the dashboard, for example, of the vehicle so that the operator of the vehicle will be alerted to the worn brake condition.