Dog whistle

http://www.ohmslawcalculator.com/555-astable-calculator

• C: 0.1uF
• R1: 0
• R2: .25 kΩ

Also

• 555
• push button
• battery
• battery clip
• piezo speaker
• 10 uF cap to isolate speaker

I could also put one of the 5k pots in series with the .25k resistor to bring the range down to human hearing