Abstract
Devastating natural disasters are prompting the need for effective early warning systems. The warning systems relying on cables or batteries are much expensive and not suitable for low-lying areas or remote environments. This research proposes a water-triggered sensor that has no energy consumption in dry conditions while becoming activated in the presence of water. The sensor is self-powered by a switchable galvanic battery which is made of two metallic electrodes isolated by an ion-loaded xerogel. When the battery is subjected to a water environment, the rapid hydration of the xerogel arouses the redox reaction between two electrodes, subsequently outputting the electrical power to trigger the sensing system associated with timely signal generation and transmission. To ensure adequate stability and durability against the ambient humidity variation, the battery is sealed with a polymer coat which is inert to the moisture but permeable to water. Since the sensor can be built on a paper base, it is suitable for Miura origami which is beneficial for improving the output power and minimizing the sensor size. Outdoor experiments confirm that the sensor is able to rapidly discriminate floods and warn nearby people and remote-control centers.