Sure - see this tutorial
I have the same code running to make an alarm, altho I added a simple external MOSFET amplifier to make it much louder.
I am adjusting the amp now - playing with a relay to make a hi/low volume kind of setting.
Am also adding a series capacitor between the gate resistor and the MOSFET, along with a resistor to ground (pulldown resistor), so that when the arduino stop sending notes the MOSFET wil be turned off by the pulldown resistor.