Catch is; get ECO MODE in Altis-AT or 6 speed gearbox in Altis-MT. AT cars are known to be less fuel efficient and this "ECO MODE" thing is there to make it better
New automatic cars (all over the world) now have better fuel consumption than manuals. The Eco mode tells you when your car is consuming the least fuel (below 2000 rpm usually). The Eco light turns on when you're driving below that rpm.
The Super ECT automatic gearbox if driven inside the eco zone gives 14.06 km/l whereas the manual gives 14.01 km/l on the new Altis.
There is no device or anything that makes your car consume "less" fuel. It's how heavy footed you are with the accelarator that defines your car's fuel consumption. Drive the car less torridly and the consumption efficiency will shoot up.