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very loud alarm help please

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If the supply voltage is more than 6V then you are straining the poor little 555. It is not designed to drive an 8 ohm speaker. A power amplifier with a fairly high supply voltage will drive an 8 ohm speaker loudly.

With a 6V supply, the output power of the 555 into an 8 ohm speaker is only about 1/2W.
The 10uF output capacitor reduces the output at frequencies less than 10kHz. It will sound like a little squeak.

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An LM386 amplifier IC has an output power of only 0.5W into an 8 ohm speaker with the square-wave signal from a 555 oscillator. Exactly the same power as from the 555 directly into the speaker.

A piezo beeper like in smoke alarms has a built-in oscillator/driver that automatically tunes itself to the loudest resonance frequency of the piezo and its tuned case. It makes a single frequency.
A piezo speaker needs to have an oscillator circuit to drive it. It has a few resonant frequencies that are loud and many frequencies that are not loud. Therefore it makes a poor siren sound.

Use a re-entrant horn speaker driven by a power amplifier.

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