Chicago has simply "tuned-up" its gas-fired boilers and is now saving $1.65 million in gas bills, while reducing CO2 emissions by almost 8,000 tons every year. These boilers account for 75% of the City’s annual gas consumption. When they are running inefficiently they consume more, so the City has arranged for engineers to overhaul the machines. Part of this includes the installation of monitoring devices which send out SMS messages reminding building managers that the machine is losing efficiency. Energy savings of up to 12% have been made in some boilers.