Check out the Utilitech Z-Wave Siren, runs on 4xD batteries and lasts many years with a selectable alarm volume upto 100db.
Also check out the Vision ZWave Siren with runs on 4xAA batteries 
with more features like adjustable auto shut off, Siren and Strobe mode and an adjustable alarm volume upto 105dB. While it works with the stock DTH for basic functionality you need a custom DTH to access advanced functionality.
Both have the ability to runs of an external power adapter.