Piezo audio indicators are low frequency

TRANSDUCERS USA FLIP Series (Frequency-Low, Indicator-Piezo) low frequency piezo audio indicators contain a solid-state piezo ceramic bender, instead of the electro-mechanical device, which incorporates a coil that creates the magnetic field to drive a hammer and hit a membrane that actuates the buzzer. Device actuates its buzzer when voltage is applied to the piezo device itself.  Without moving parts, device delivers a longer life and lower failure rate.