How to amplify alarm clock buzzer?

The ones I've seen use a piezo-electric "buzzer". This makes a sound when a voltage is applied to it, usually at 1 or 2 KHz. There should be an electrical signal of this frequency in the circuit. Just condenser couple this to any sort of amplifier/speaker.
If you want a different frequency, use the signal to the "buzzer" to trigger your own free running flip-flop running at the desired frequency. You could even get fancy and switch on any desired audio signal, from a radio or such.
My old ears have a hard time hearing that "buzzer", so I might try it myself! :-)

Thanks for the insight. That might be part of the problem for me, too. But the biggest problem is that I wear earplugs at night. So I do not hear the alarm at all :-(.
Let me know if you design a circuit for yourself :-).
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There won't be "a" circuit. Different alarm clocks will have different solutions. A "mechanical" quartz crystal clock will probably have a pair of contacts that close when the set time is reached. Some "electronic" clocks will have single-ended sounder drive and some will have push-pull. Some may have a light/LED that illuminates when the alarm sounds, and it may be easier to interface to that.
Of course alarm clocks themselves vary greatly in alarm volume anyway. IIUC, it is possible to get an alarm clock with a 115dB sounder - loud enough (almost) to wake the dead.
-- Sue

too. But the biggest problem is that I wear earplugs at night. So I do not hear the alarm at all :-(.
Kind of like wearing a sleeping mask because the light is too bright?
Anyway, is some kind of transducer, perhaps a guitar contact pickup to operate a VOX (voice activated switch). The switch can then operate some device to wake you up: a fan or a massage mat.
Then again, you could attach it to a motor, which will wind up a string, which can pull the earplugs out
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Thanks for the insight. That might be part of the problem for me, too. But the biggest problem is that I wear earplugs at night. So I do not hear the alarm at all :-(.
Then why not buy a clock with an under-the-pillow vibrator? Some have a powerful light as well.
John (deaf-ish)

When I was a kid, if I really needed to wake up after a late night out with my band, I used an intermatic timer to turn on my Ampex reel-to-reel and Scott receiver which would then blast Jeff Beck's Rice Pudding our of my JBL L100's. Mom was a big fan of that.
peace dawg

Use the alarm to make my hospital bed move. ;-)

For crying out loud, What do you think this is ? an Electronic Design Group....
Why bother with sounds - Since you wear earplugs anything sonic will not be enough -
The best we can do for you is to suggest you remove the speaker attach the output to the input of a DC solid state relay., on the normally off output contacts you add a 110AC line - Splice the Neutral & place it with medical padded contacts to your forhead., then run the Hot line with relay in series and place that on your feet.
When the alarm goes up you'll get a nice jolt of household current and wake up...don't forget to apply plenty of conductive jell to the pads to insure they won't fall off in your sleep and that they make good contact with your skin ;-)
UV_Ray Just Passing Through