I just finished the process of replacing our access control system. I can tell you 1 thing, do not go with Protection 1 for access control. The system is horrible.
We opted to go with Genetec ( »www.genetec.com/Pages/default-en.aspx
) to replace the mess ADT left us with and we couldnt be happier..!!
It is a complete solution for access control and surveillance. Of course, you can just pick and choose whatever area you wanna implement. This system is all IP based so if you have multiple sites, you can just use your VPN to control doors and access. All the access information is stored in the controllers so if you lose your VPN, the doors can still operate with the latest data that was synced.
We only have 1 site, but looking at the software, there was ways to partition the system so that it logically separates X amount of locations.
If you have any specific questions, let me know. I know how much of a pain is to research these systems.