Emerging feedback systems based on tracking body conditions can save human lives. In particular, vulnerable populations such as disabled people, elderly, and infants often require special care. For example, the high global mortality of infants primarily owing to sudden infant death syndrome while sleeping makes request for extraordinary attentions in neonatal intensive care units or daily lives. Here, a versatile laser‐induced graphene (LIG)‐based integrated flexible sensor system, which can wirelessly monitor the sleeping postures, respiration rate, and diaper moisture with feedback alarm notifications, is reported. A tilt sensor based on confining a liquid metal droplet inside a cavity can track at least 18 slanting orientations. A rapid and scalable laser direct writing method realizes LIG patterning in both the in‐plane and out‐of‐plane configurations as well as the formation of nonstick conductive structures to the liquid metal. By rationally merging the LIG‐based tilt, strain, and humidity sensors on a thin flexible film, the multimodal sensor device is applied to a diaper as a real‐time feedback tracking system of the sleeping posture, respiration, and wetness toward secure and comfortable lives. User‐friendly interfaces, which incorporate alarming functions, provide timely feedback for caregivers tending to vulnerable populations with limited self‐care capabilities.

Skin‐like wearable sensors are regarded as key technologies toward home‐based healthcare, human–machine interfaces, robotics, prostheses, and enhanced augmented/virtual reality (AR/VR). Inspired by human somatosensory functions, artificial sensory feedback systems play vital roles in shaping interactions with complex environments and timely decision‐making. This study presents an overview of recent advances in feedback‐driven, closed‐loop skin‐inspired flexible sensor systems that make use of emerging functional nanomaterials and elaborate structures. Drawing on feedback solutions, four categories of sensor systems are highlighted, which include prosthesis‐ and AR/VR‐based human–machine interfaces, smartphone‐based approaches for point‐of‐care detection, and smart wearable displays for direct signal visualizations. Furthermore, the progress of machine learning on the reliable recognition of massive quantities of signals generated by flexible sensor networks is briefly discussed. The state‐of‐the‐art hybrid sensor techniques, along with other emerging strategies, will enable total sensory feedback loop systems to be developed for next‐generation electronic skins.

In the past decade, the global industry and research attentions on intelligent skin-like electronics have boosted their applications in diverse fields including human healthcare, Internet of Things, human–machine interfaces, artificial intelligence and soft robotics. Among them, flexible humidity sensors play a vital role in noncontact measurements relying on the unique property of rapid response to humidity change. This work presents an overview of recent advances in flexible humidity sensors using various active functional materials for contactless monitoring. Four categories of humidity sensors are highlighted based on resistive, capacitive, impedance-type and voltage-type working mechanisms. Furthermore, typical strategies including chemical doping, structural design and Joule heating are introduced to enhance the performance of humidity sensors. Drawing on the noncontact perception capability, human/plant healthcare management, human–machine interactions as well as integrated humidity sensor-based feedback systems are presented. The burgeoning innovations in this research field will benefit human society, especially during the COVID-19 epidemic, where cross-infection should be averted and contactless sensation is highly desired.

A disorder in the thermoregulator center in a human body leads to some potential diseases such as fever and hyperthyroidism. To predict these diseases early, monitoring the health condition of the human body due to the influence of thermoregulation disorders is important. Although extensive works are performed on sweat‐rate detection by constructing microfluidic channels, skin‐moisture evaporation before sweating remains unknown. This work proposes a wireless and flexible sensor sheet to investigate the thermoregulatory responses of different people under cold stimulation and exercise by measuring the temperature and moisture variations on the finger skin. An integrated flexible sensor system consists of a ZnIn2S4 nanosheet‐based humidity sensor and carbon nanotube/SnO2 temperature sensor. The results exhibit distinct thermoregulation abilities of five volunteers. Interestingly, the sudden increase in finger moisture that results from the excitation by the sympathetic nerve is observed during the cold‐stimulus test. Although further studies are required to predict the potential diseases resulted from thermoregulation disorders in human body, this study provides a possibility of continuous and real‐time monitoring of thermoregulatory activities via skin moisture and temperature detection using a flexible sensor sheet.

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