The Internet of Things (IoT) is defined as a network of nodes able to monitor physical and chemical magnitudes and provide relevant information concerning safety of individuals and goods. This involves continuous monitoring to assess that a safety-relevant magnitude has not reached an alarming threshold value. Stable and reliable power sources are key factors to ensure a monitoring scenario of several months to years.

Significant efforts of continuously harvesting energy from the environment have been done in the last decade; solar, flow systems (wind and hydro), heat and mechanical harvesting have evolved to provide sufficient power to enable wireless communication under controlled ambient conditions. Nevertheless, their dependence on environmental conditions constrains their application in a very limited range of settings. This makes primary batteries the most preferred power for wireless sensor networks and today, the optimisation of low-power consumption modules allows expanding power autonomy of wireless nodes up to several years. However, the current predominance of primary batteries in the IoT scenario and the expected strong market penetration of sensing modules allow foreseeing a huge production, usage and disposability of battery components that depicts a rather non-ecofriendly panorama.

ECOTAGS project aims to develop a new paradigm of assessing alarm monitoring in wireless nodes with a zero-energy consumption strategy. The main idea is to utilise phasechange materials (PCM) to harvest the variation of energy involved in a particular environmental change to be recorded. Phase changes from liquid to solid have been used historically to drive actuators that respond to thermal, pressure or light stimulus among others.

ECOTAGS takes advantage of solid to liquid phase changes of a PCM to convert a change in a physical parameter of the surrounding environment into electrochemical energy by using the originated liquid phase to activate a single use paper-battery. The activation of the battery allows generating a pulse of electrical power that can be used to send an alarm signal to a remote receiver by radiofrequency data transmission. In this way, the battery-PCM system remains inactive until the PCM harvests sufficient energy from the environment to become liquid. Contrarily to the current IoT paradigm, this system would consume no power unless an alarming event takes place, thus using the electrochemical energy stored in the battery only when the system possesses relevant information to report. With the proposed technology, we aim for multiple applications which extend from fire, light, pressure, gas, or radioactivity detectors in buildings, parking areas, research facilities, factories, transportation, and forests among the most relevant. The detecting tags have the potential of being low cost, environmentally friendly and yet smart, so they would allow ubiquitous monitoring of large spaces for extended periods of time.