Two slightly underfed German Shepherds work the best.
With that said the fact is, it is not the alarm as much as it is the monitoring.
Well that and design/install.
When designing a system one needs to think like a thief.
I always ask myself: How would I break into here; when I design one.
The other factor is location.
Location of the site plays into police and fire response.
The larger the city or town/the longer the response time.
See line one.