Event-Fusion at the Edge: A Low-Cost Smart Doorbell with Quantified Notification Latency

This paper presents a low-cost, edge-centric smart doorbell that converts a brief doorway interaction into timely, image-based awareness. The system fuses explicit human intent (a momentary doorbell press) with an anticipatory passive-infrared (PIR) motion cue and executes the resulting event pipeline entirely on a Raspberry Pi 3B+ with a CSI-attached camera, an LCD for local status, and a buzzer for immediate acknowledgement. We formalise the control logic through a short temporal fusion rule and a debounce/throttling condition that governs notification cadence, and we decompose end-to-end delay into device and network contributions to make latency tunable and measurable. The prototype operates as a coherent, event-driven service: on a valid trigger, it captures a still frame at the interaction moment and dispatches a standards-compliant email message (MIME over SMTP with STARTTLS). Evaluation at two residential entrances shows robust PIR detection from 1–4 m in daylight and a practical 1–3 m envelope under porch-light conditions. Notifications typically arrive within a few seconds; across repeated trials the lower quartile clustered near 4 s, the mean was ≈9 s, and right-tail outliers were attributable to network and mail-server processing rather than device overhead. The bill of materials remained ≈250 MYR, yielding functionality comparable to commercial devices at a fraction of the cost. Beyond a reproducible reference design, the work contributes a compact, testable fusion law, a transparent latency model, and instrumentation that ties user-perceived performance to specific architectural choices, while outlining upgrades in illumination, sensing, and privacy for future deployments.