A new development from the “Wireless & Transponder Systems” business unit provides protection against unwelcome houseguests. Known by the name of “HomeGuardian,” a fingernail-sized radio sensor is fitted between the glass pane and the aluminum profile which can detect the state of a window – whether it is open, closed or tilted. The sensor draws the energy it requires from its surroundings and can be operated wirelessly and without a battery. “The challenge was to develop a wireless and maintenance-free sensor that detects the state of a window and transfers this data securely and reliably via radio transmission,” explains Gerd vom Bögel, head of the business unit “Wireless & Transponder Systems” at the Fraunhofer IMS. The “HomeGuardian” – unlike other window sensors available on the market – carries out its detective duties entirely energy self-sufficiently and detects attempted break-ins by differentiating various vibrations, which, for example, can be caused by a break-in attempt with a crowbar at the window frame. The goal, to develop an energy self-sufficient sensor to monitor the status of windows and doors, was preceded by the selection of a suitable energy harvester. In this case a small but efficient solar cell in combination an energy management system, a power storage and a particularly energy-efficient radio frontend makes it possible to operate the “HomeGuardian” in its job against burglars.