Having it auto dial 911 will most likely result in you getting charged!
A disarm signal stops the dialing process as well as the alarm.
Yes, often times false alarms will trigger a fine from the police department. This wasn't always the case, but some time ago in New York they got tired of motion sensors that triggered from the family cat 6 times a week...
Also in some jurisdictions, you need an "alarm permit" for any auto-calling alarm. If you have it call your neighbor, or your cell phone, and then a call to police is made, that is exempt.
Personally I am trying to get to the point where the alarm/motion will trigger an email picture of the offending motion. I will then decide if it's the cat, UPS guy outside, or Al Quaida