"Key on" is a phrasal verb that means to turn on or activate something by using a key or similar device. Some alternative synonyms for "key on" include "switch on," "ignite," "start up," "power up," "activate," "engage," "fire up," and "kickstart." Each of these phrases conveys the same essential idea of causing a device, engine, or other mechanism to come to life. Additionally, "key in" is sometimes used as a synonym for "key on," which may be more relevant when referring to entering data or programming a device using a key or keypad.