Researchers at the Fraunhofer Institute for Microelectronic Circuits and Systems in Germany have developed a smart radio sensor chip that is completely solar-powered and monitors your window to remind you if you've left it open.
This tiny little chip is designed to be mountable on the aluminum frames of windows, between panes of glass. Its top surface is sheathed by a solar cell, and it is capable of storing enough power during daylight hours to stockpile energy to let it operate all night long.
This radio sensor chip is embedded with an accelerometer and magnetometer that allow it to detect when a window has been opened and by how much. If the window has been left open too long, the chip sends a signal to a base station, which alerts the homeowner.