Sample paper
Word Count: approximately 2,000 words
Scope Statement
The report provides a requirements analysis and specification for the detection and alert subsystem of an automated home security system, responsible for real-time monitoring, threat detection, and alert notification related to unauthorised entry. Specification artefacts include data flow diagrams, control flow diagrams, process specifications, and control specifications, aiming to unambiguously capture functional, behavioural, and performance requirements to guide subsequent design and development.
Subsystem Description
The subsystem integrates motion sensors, door and window sensors, glass break sensors, and security cameras, processing sensor data in real time against the system's armed/disarmed state, activation type, sequence and timing, and camera-based visual confirmation. Five operating states govern behaviour: Disarmed, Armed Stay (perimeter sensors only), Armed Away (all sensors monitored), Alarm Pending (entry-delay countdown following a triggering event), and Alarm Activated (full alerting once the countdown expires without a valid disarm). Alert channels on activation include an audible siren and flashing light, push notifications, SMS and auto-dialer calls to the homeowner and emergency contacts, and event/video transmission to a professional monitoring service. Performance requirements mandate critical sensor sampling at 10Hz or better, door/window checks at least once per second, threat assessment within 500ms, and alert transmission within 1 second of confirmation, supported by distributed edge processing, a real-time operating system, and multi-modal alerting for redundancy.
Refining the Description with Generative AI
Initial AI-generated responses to queries on functional components and performance requirements captured the high-level architecture accurately but omitted several elements later added: specific sensor types and placement, mobile app remote control, hybrid edge/cloud processing with machine learning-based threat assessment, professional monitoring dispatch as an alert channel, encryption and secure API integration standards, and -- critically -- the explicit state model (Armed Away, Armed Stay, Alarming) and its triggering events, which is central to defining the subsystem's real-time behaviour and was reframed as the end-to-end flow from sensor activation through threat assessment to alert generation.
Data Flow Diagrams
The context diagram establishes the subsystem's scope and external entities. The Level 1 DFD decomposes it into five processes: Sensor Data Acquisition, Monitoring Mode Control, Threat Analysis, Activity Log, and Alert Generation. A Level 2 decomposition of Threat Analysis further breaks it into Motion Analysis, Entry Point Monitor, Glass Break Assessment, and Threat Level Determination, with sensor inputs flowing into each specific subprocess before contributing to a final threat-severity decision.
Control Flow Diagrams
The Level 1 CFD layers control flows onto the data model: Arm/Disarm Commands change system state; a Threat Detected signal activates Alert Generation only when the system is Armed Away or Armed Stay; Alarm Timeout signals entry-delay expiry without a disarm event; Alarm Deactivated cancels an active alarm on valid passcode entry; and Sensor Fault signals a missing sensor heartbeat indicating potential malfunction.
Process Specifications
The Assess Threat process specification takes motion, door, window, and glass-break sensor states plus the current arm state as inputs, evaluating branching logic specific to each arm state: in Armed Away, an open door or window or a glass-break event sets an Active Threat, while motion alone sets a Potential Threat; in Armed Stay, only door/window and glass-break events register (interior motion is ignored), each setting an Active Threat.
Control Specifications
The state transition diagram and its tabular equivalent define transitions across Disarmed, Armed Stay, Armed Away, Alarm Pending, and Alarm Active states. Arming from Disarmed starts an exit-delay timer; a triggering sensor event while armed starts an entry-delay timer and moves to Alarm Pending; a valid disarm passcode during Alarm Pending cancels the timer and returns to Disarmed; and entry-delay timer expiry without a valid disarm transitions to Alarm Active, simultaneously activating the siren, sending a smartphone alert, and contacting the monitoring service. A valid disarm from Alarm Active deactivates the siren, cancels the smartphone alert, and notifies the monitoring service of resolution.
Conclusion and Next Steps
The analysis captures the core functional, behavioural, and performance requirements for the subsystem, with data and control flow modelling decomposing its logical components and the process and control specifications detailing internal logic and state transitions. Recommended next steps include stakeholder validation, elaboration into detailed technical specifications, architectural and detailed design, technology selection, prototyping, comprehensive testing, integration with other smart home subsystems, and user acceptance testing. Future enhancements could include AI-based visual threat confirmation via camera feeds, two-way voice communication with the monitoring service, and integration with other smart home functions such as automatic lighting and door-locking on intrusion detection.
References
Honey, G. (2007). Intruder alarms. Elsevier. Kopetz, H., & Bauer, G. (2003). The time-triggered architecture. Proceedings of the IEEE, 91(1), 112-126. Laplante, P. A. (2004). Real-time systems design and analysis. Wiley. Pressman, R. S. (2005). Software engineering: a practitioner's approach. Palgrave Macmillan. Soloway, R. L., Hevia, J. D., Karl, T. F., Carrieri, M. A., & Buccola, C. S. (2004). U.S. Patent No. 6,812,836. U.S. Patent and Trademark Office. Veľas, A., & Boroš, M. (2019). Intruder alarms. EDIS.