You could have 1 sound per DC8/EB8 outlet you're willing to use.
For example, you could use different sounding siren's for PH vs Temp, or high/low condition of either and just program the outlet to turn on/off based on the variable being monitored.
My "alarm" is a cheap 110v buzzer that cost less than $3 at a local surplus store, but you could make one for $10-20 with bits from RadioShack as well.
Chris