The ECON button turns the ECON mode on and off.
The ECON mode helps you improve your fuel economy by adjusting the performance of the engine, transmission, heating system*/climate control system*, and cruise control*.
Honda Civic Owners Manual. Using the Smart Entry with Push Button Start System
When you carry the smart entry remote, you
can lock/unlock the doors, fuel fill door, and
open the trunk.
You can lock/unlock the doors and fuel fill
door within a radius of about 32 inches (80
cm) of the outside door handle. You can open
the trunk within about 32 inches (80 cm)
radius ...