Since I had water in my basement I build a water detection device with a arduino nano, a water level sensor and a piezo buzzer. Everything is powered by a 9v battery. My problem is that the buzzer is to quiet. I need something louder that I can hear upstairs. I'm quit new so maybe someone can help to find a better solution to produce a louder sound with my arduino nano.
Thank you for your time.
Max 
9V transistor battery has low current and then the Arduino regulator wastes 4/9ths of that.
Still, if you use a transistor to drive the buzzer directly off 9V power it should make a lot more racket.
Servo-operated air-horn.
You have to pick the piezo buzzer to fit your requirements, not just price.
I used one left by a customer on a discontinued product, it is so loud it hurt to test it and it ended up in a sealed metal box to quite the sound. Runs on 5 volts.
Paul
Whatever is in my smoke alarms works really well.
Since this is an ongoing alarm I would use a different battery that is rechargeable then keep the battery charged with an A/C adapter so no loss of alarm if the power goes out
A bigger Piezo buzzer.
