If you use a USB connection for 5 V power and have arelatively high impedance speaker, like a 64 ohm headset driver, another option is an AC series CMOS hex inverter Schmitt trigger, the 74AC14. One inverter is the oscillator, and the other five drive both ends of the speaker in a BTL (bridge-tied load) configuration.
1 - 74AC14
1 - 10K resistor
1 - 0.1 uF capacitor
1 - speaker
Output frequency = 450 Hz.
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