I used to have a Viper talking alarm on my Boxter but it was too obnoxious. "System armed" ect.. I prefer the chirp.
Most aftermarket alarms serve the purpose and you don't have to pay a lot of $$$ for a good one.
I have a 900 MHZ Compustar two way system.
www.compustar.org
Also
www.asianwolf.com has some reasonable two way FM alarms and add ons.
I did install it myself. I'm an Electrical Engineer so I have a slight edge.