A communication system is provided that can be added to a legacy alarm system to provide a plurality of communication modes to a remote server system from the legacy alarm system and provide remote control and monitoring to a user of the system via two-way communication links. The communication system can be configured to communicate with an alarm processor of the legacy alarm system through use of a keypad bus typically used by the legacy alarm system for communication between the alarm processor and one or more keypads. Communication modes that can be provided by embodiments of the present invention can include, for example, communication over a public switched telephone network, cellular transmission, broadband transmission, and the like. The communication system can monitor all configured communication modes and determine which communication mode is the best for providing communication between the alarm system and the remote server. Through these communication modes and by virtue of being coupled to the alarm processor via the keypad bus, the communication system can provide both transmission to the remote server of the status and alarm condition of the legacy alarm system as well as provide control signals from the remote server to the legacy alarm system. The remote server provides pre-determined responses to information received from the alarm system, including providing alarm system condition information to a user or a monitoring station for response.