The application of the CrackGuard sensor is as follows; during a regular inspection a surveyor detects a crack in a web of crude oil tank. In his judgment the crack has an acceptable length but he knows that this crack may grow further and may become critical. He does not know when this will happen. So, he first decides to apply the CrackGuard sensor which will notify him (or/and the operator) when the crack reaches its critical length. Secondly, he assigns an ID to it and continues its survey. After that, he could have find multiple cracks of acceptable length in several tanks. Therefore, at the end of his survey he will probably install a network of CrackGuard sensors = the CrackGuard system. Finally, the system will check periodically (e.g. monthly) the status of individual CrackGuard sensors and send the data to a remote location (surveyor/operator office). Other working principles are also possible but this will be worked out in the project.