Simple yellow Post-it notes with the message "When not in use, turn off the juice," pointedly left on classroom computers, printers and air-conditioners, have helped one public school district in New York save $350,000 annually on utility bills.

Energy consumption across New York City's 1,245 school buildings is down roughly 11 percent since 2008, as motion detectors have been installed on classroom lights and unused refrigerators and freezers have been unplugged for the summer.

The money saved on energy is also being used to buy energy-efficient windows and boilers in one school district.

(READ more in the NY Times)