With the continuous growth of the Internet of Things (IoT), the trend of increasing numbers of IoT devices will continue. To increase the network's capability to support a large number of active devices accessing a network concurrently, this work presents IoT-ResQ, a warm-started quantum annealing-based multi-device detector via quantum reverse annealing (RA). Unlike in typical quantum forward annealing (FA) protocol, IoT-ResQ's RA starts its search operation on a controllable candidate classical state, instead of a quantum superposition, and thus allows refined local quantum search around the initial state. This procedure can provide an opportunity of utilizing both conventional classical- and quantum-based detectors together in a hybrid synergy, to boost quantum optimization performance, mitigating the effect of quantum decoherence and noise on quantum hardware. In our evaluation, IoT-ResQ achieves nearly two to three orders of magnitude better BER and over 2X packet success rate with packet size of 32-byte compared to other quantum and conventional detectors at SNR 9 dB to support 48 active IoT devices with QPSK modulation (implying 48,000 deployed devices with 0.1% wake-up radio rate at a time), requiring 140 μs pure compute time for detection.