0 Electronic dog whistle

It is sometimes called as “ultrasonic dog whistle” since the sounds produce is very high frequency that human ear can’t hear.  Human hears sounds with frequency from 20Hz up to 20 kHz, dog on the other hand has a wider hearing range- from 40Hz to 60 kHz (via Wikipedia.org).
The circuit below is an electronic whistle powered by 555 timer IC. The circuit can produce sound around 24khz.

Dog whistle circuit diagram

Part list:
R1 - 2 kilo ohms 1/4W
R2 - 2 kilo ohms 1/4W
C1 - 10nF mylar or ceramic
C2 - 100nF
C3 - 220nF
peizo - peizo speaker or speaker that is good in high frequency (tweeter)
DC - 6V to 12V battery
555 IC

Parts digrams: click to Enlarge

555 pins

Peizo speaker

Note: You can adjust the frequeny of the circuit by just replacing the values of R1, R2, and C1 using the monostable 555 calculator.