Event-driven cameras are well suited for always-on edge vision, but forwarding all events creates unnecessary overhead. Events outside user-defined ROIs are semantically irrelevant, while many ROI events arise from background motion, lighting changes, or sensor noise rather than meaningful activity. We propose SENTRY, a near-sensor pipeline that addresses both issues through hierarchical spatial reasoning. A coarse spike-rate gate discards frames with low ROI activity, while a spatially-aware confirmation stage compares each region’s activity against the global background rate to suppress diffuse noise. Evaluated on a real indoor surveillance sequence, SENTRY achieves +64% precision and − 57% false positive rate relative to a global spike-rate baseline, targeting resource-constrained, always-on platforms where energy efficiency and rapid response must be achieved simultaneously.

We present BISen, a framework for efficient and reliable convolutional neural network (CNN) inference on battery-free, energy-harvesting IoT sensor nodes. Battery-powered deployments suffer from limited lifetimes, high replacement costs, and environmental impacts, problems that will intensify as IoT scales to billions of devices. Energy-harvesting nodes remove batteries but face intermittent power, resulting in frequent failures that corrupt the intermediate CNN state, require costly checkpointing and rollback, and amplify non-volatile memory (NVM) traffic under tight on-chip memory constraints, leaving little harvested energy for useful sensing and inference. BISen introduces a reactive intermittent execution model for CNN workloads on off-the-shelf ultra-low-power microcontrollers. An energy-aware state machine with a safe-stop mechanism halts execution before brownout, while selective checkpointing preserves only the minimal CNN state needed for forward progress. This enables seamless resumption across power cycles while sharply reducing NVM reads/writes and memory-access overheads. Across two commercial MCU+radio platforms, three real harvested power traces, and nine CNNs, BISen cuts NVM operations by up to 86.4%, reduces standby/load/store operations by up to 94.1%, 94.5%, and 90.7%, and improves sensing throughput by about 1.3−1.4× compared to a state-of-the-art reactive baseline under the same energy budget, enabling long-lived, battery-free, carbon-aware IoT deployments.