Civil construction sites are considered as one of the riskiest environments where many potential hazards may occur. To protect construction workers and prevent accidents in such sites, this paper proposes a novel design for an autonomous system that monitors, localizes, and warns site laborers who avail within danger zones. The proposed system is user-friendly, and its architecture is based on Internet of Things (IoT). The heterogeneous components of this architecture are seamlessly integrated into a middleware backend online server. To accurately detect and identify construction workers, the proposed system employs three combined techniques. They are 1) the 868 MHz radio frequency, 2) directional antennas, and 3) the 40 kHz ultrasound waves. Vehicle’s rear is secured by a sensing unit that ensures good coverage along with a wearable device for workers. The design of the wearable device includes a set of components which are a radio transceiver (transmitter/receiver), a wake-up sensor, an alarm actuator, and a GPRS module. The wearable device has a power saving scheme with a current consumption as low as 0.5 μA at 3 V supply; thanks to our RF wake-up sensor. Via proximity, this wearable device becomes hybrid (active/passive) in which it remains in deep sleep mode until the presence of a radio frequency (RF) field. Consequently, the rechargeable battery’s life gets increased by up to 2 days of autonomy before recharging. Furthermore, the paper presents an implementation of wireless nodes that are powered by light energy using photovoltaic cells. These nodes adopt energy management and storage schemes for continuous operation for indoor and outdoor environments.