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.

A kirigami-based graphene–polymer hybrid nanocomposite is realized by a laser direct writing technique for reliable skin-inspired strain sensors, presenting almost no performance degradation even after >60 000 stretching cycle tests.

A Pd/HNb3O8 flexible humidity sensor is developed with long-term stability at a high humidity level (∼90% RH). Using the sensor, wireless monitoring of human respirations and finger moisture variation under exercise is successfully demonstrated.

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.

The next generation of electronics will include human-interactive flexible sensor sheets to monitor health. One approach is to realize practical macroscale low-cost sensor arrays to monitor pressure distribution and health conditions without directly attaching a device onto the body. However, practical requirements such as reliability, scalability, and washability are not often discussed as most studies focus on the sensing sensitivity and validations. This study demonstrates an all textile-based tactile force sensor sheet that covers the above requirements. By considering the device design and materials, high reliability/repeatability (≈250 000 cycles at ≈5 kPa) and washability are realized. These are important factors for practical applications for human-interactive macroscale sensor sheets. In addition to the fundamental characteristics, pressure distribution mapping and respiration rate monitoring are confirmed by placing the sensor sheets on a bed, chair, and floor.

Continuous multiple data health monitoring has high potential to detect abnormal conditions or early stages of diseases in the future. To monitor a continuous small vital signal, one of the promising architectures is an attachable flexible multimodal sensor system, which can detect multiple health conditions from the skin surface. Recent breakthroughs have realized continuous sweat chemicals or physical conditions using flexible sensors. However, multimodal sensor integration to monitor chemical and physical information simultaneously and precisely is still a challenge. In this study, we present a multimodal wearable sensor sheet, which allows us to monitor sweat glucose, electrocardiograms, and skin temperature. Furthermore, to prevent the accumulation of glucose on the sensor surface for precise monitoring, a fluidic channel is also integrated to refresh the sweat from the sensor surface, resulting in the precise measurement of chemical substances in real time. This multimodal and flexible sensor platform takes a significant step toward realizing wearable healthcare applications to diagnose the early stages of diseases in advance.

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systems for IoT, economical fabrication of devices is important. At a minimum, flexible devices currently require signal processing circuits and batteries to operate sensor systems. Integrating these into a sensor while maintaining mechanical flexibility is difficult without increasing the device cost. An approach to overcome this challenge is to separate the sensor system into two film parts: a disposable one for the printable low-cost sensor array and a reusable one for the expensive systems, including circuits, battery, etc. [1-3] Because the connector combining these two components is usually inflexible, mechanical flexibility is often sacrificed. Our group has reported a flexible connector, which electrically connects two flexible sheets (i.e., disposable and reusable sheets) without sacrificing the mechanical flexibility using a liquid metal of eutectic Gallium Indium (EGaIn). [13,14] However, the metal can be readily removed from the connector by scratching it due to the liquid-state of EGaIn at room temperature, which is impractical for IoT applications including human-interactive devices. An interesting approach for sensor applications is to monitor the chemical distribution in a solution for environmental monitoring and even healthcare diagnosis from sweat. Although many studies have monitored the chemical contents in sweat for healthcare and medical applications, [1-9] chemical mapping in a solution using a flexible sensor sheet has yet to be demonstrated. If a flexible chemical sensor array is realized for mapping, applications can be expanded from healthcare/medical to biological and environmental monitoring. Such an array should also be able to map interesting data from an object for the next class of IoT concepts, which has been very difficult to collect using conventional inflexible chip-based sensors. To address the above challenges, this study proposes mechanically flexible and stable macroscale pH distribution and diffusion monitoring in solution with a flexible electrical connector. Figure 1a shows the device concept. First, a flexible connector using a soft 3D Ag electrode is discussed. As a reusable sheet, flexible extended gate ion-sensitive field-effect transistors (ISFETs) are fabricated using thin-film InGaZnO for the n-type transistors. There are two reasons to use ISFETs for pH monitoring in this study. The first one is to show the possibility