"i need something around 100 Db, i suppose it cant do."
Well, 100dB... at a distance of 1cm or 1km?
Headphones or 30cm woofer?
Frequency range desired?
If you CRC your output signal (AC coupling then filter off nasty squre edges) then feed an audio amplifier you can get what you want as hippy alluded to above.
If you want to drive anything more than a tiny speaker at a decent power you will probably have to supply a lot more than 5V to the speaker.
The minimalist may suggest a home-brew using one or more transistors. I wouldn't bother as there are a zillion audio amplifier available. These range from ic chip size devices (some SMD like TI's TPA1517), through various modules with heat-sinks right up to PA system monsters.
Having said that a transistor amped piezo (in resonant enclosure) may give a satisfying sound over a limited F range and at shot range, but it won't be much use as a burglar alarm!
The efficiency can be improved hugely by some effort from you. If you have a standard cone-type speaker dangling in mid air the output will be poor, but the same speaker in a well designed enclosure will be much, much louder and with a much better frequency response.
An example of an easy-to-use (apparently) device which could handle a small/mid sized speaker is the TDA2003 from ST. But there are many other options which you can search for yourself. And then the horrible part... you will have to read the Data Sheets