An energy-efficient sensor node processor (SNP) is presented for intelligent sensing in Internet of Things (IoT) applications. To achieve ultralow energy consumption and satisfying performance, the proposed processor incorporates an ARM Cortex-M0 RISC core and diverse hardware accelerators, including discrete wavelet packet transform engine, finite-impulse-response filtering engine, fast Fourier transform engine, and coordinate rotation digital computer engine, to accelerate signal processing tasks. At the architecture level, dual-bus architecture with automatic bus sensing and reconfigurable memory access scheme are proposed. At the circuit level, digitally assisted cognitive sampling and ultralow-voltage operation with in situ timing-error monitoring techniques are employed. When applied to neural spike classification and vehicle speed detection, the proposed SNP consumes only 39 and 29 pJ/cycle, respectively.