Wearable and Internet of Things technologies represent a potentially high-impact breakthrough for next future strategies targeting improved occupational safety and health management. In particular, they could enable the real-time monitoring of health-related and environmental information to the wearer, emergency responders and inspectors regarding air pollution, indoor air quality, aerosol exposure and detection of biothreat agents in the workplace. Among hazardous gaseous compounds causing severe health issues, ammonia shows a high solubility in aqueous environment and the contact with its vapours immediately causes irritation to eyes, mucous membranes and whole respiratory system, while exposure to high concentrations can lead to life-threatening conditions. This contribution describes the development of a wearable gas sensor for NH₃ detection at room temperature [1] based on the organic semiconductor poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS), electrochemically deposited iridium oxide particles (IrOx Ps) and a hydrogel film based on agarose that assists the sensing mechanism, which relies on electrochemical gating [2-5]. The working principle significantly differs from most of the state-of-the-art NH₃ gas sensors and originates from the potentiometric response of IrOx Ps, which are embedded within the organic semiconductor and respond to local pH variations in the hydrogel, thus modulating the doping state of the semiconductor. The hydrogel interface, where the gaseous analyte reversibly absorbs and dissolves producing pH variations, is actually the key component of the sensor structure for the achievement of a reversible and selective response. Its composition, acid-base properties and morphology were finely optimized to obtain self-healing properties, as well as the desired porosity, adhesion to the substrate and stability to humidity variations. Thanks to the reliability of the analytical response, the simple two-terminal configuration and the low power consumption (around 0.1 mW), the PEDOT:PSS/IrOx Ps/hydrogel sensor was realised on a flexible plastic foil and successfully tested in a wearable configuration with wireless connectivity to a smartphone. The wearable sensor showed stability to mechanical deformations and good analytical performances, with a sensitivity of 60 ± 8 μA decade^-1 in a wide concentration range (17 – 7899 ppm), which includes the safety limits set by law for NH₃ exposure, e.g. 25 ppm averaged over an eight-hour workday and 35 ppm for short-term exposure (according to the National Institute for Occupational Safety and Health).