I am pretty new to all that stuff.
So far I have experimented with 555 at 10-25 kHz, but the dB is too low. Even at 10 kHz the output power is pretty low (measured by my Samsung app, Oscope at 2-4 cm distance it's just a few dB). I am using a piezo transducer from an old sound system, no spec, just a piezo disk 2.5cm diam with two leads black and red).
My question : Is it possible to turn an old smoke alarm into an Ultrasonic Dog Replant?