1) In order to set up a static IP address for the alarm controller, you will need to know...or obtain....the MAC Address of the alarm controller device.
There may be more than one MAC Address depending on how the alarm controller connects.....using either wireless or Ethernet. Which is it?
The MAC Address is usually listed on a label on the back or bottom of the device and it looks something like this, for example only:
A1:B2:C3:D4:E5:F6
2) Your alarm controller may likely be expecting to connect to a router that uses Universal Plug and Play (UPnP), which automatically opens the ports that the device requires. Unfortunately, the Apple routers do not support UPnP......which creates a lot of difficulty for users who are trying to do the type of thing that you are trying to do. Lack of UPnP may be a show stopper depending on your alarm device.
Sometimes, the Apple router can be configured using what is known as manual Port Mapping. In order to do this, you would need to have or obtain all of the various port setting values for the following ports:
Public UDP
Public TCP
Private UDP
Private TCP
When you have the info for both 1) and 2) above, post back and we will continue. It would be very helpful if you could provide a link to the setup guide or installation manual for the alarm controller.