Where sensors act as the nerve endings of an alarm system, controllers act as the brain and take information from the sensors and process this into a code that alerts the central monitoring station about what part o the monitored area is being intruded on.
Controls can connect to the central monitoring station in a couple of ways. High-end systems, such as those in many government buildings and school campuses, use direct phone wires, or tamper-resistant fiber optic cable. In recent years a more common approach has been the use of digital telephone dialer units to dial the central station via the Public Switched Telephone Network (PSTN) and signal the alarm with an encoded message string or synthesized voice that the central station can decode. The call terminates any other active calls from the premises and takes the priority. Many systems are equipped with a backup dialer capability in the event the primary PSTN circuit does not function.
Most recently, voice over IP technology is being used to drive broadband signaling for alarm reporting. Older analog systems can be migrated to broadband with the addition of an alarm server device that converts telephone signals or data port traffic into IP messages that are able to be used with broadband transmission.