Aware of what is going on or what is up to date. If you describe someone as switched-on, you mean that they is aware of the latest developments in a particular area or activity. Informal: 'I am very impressed with Bob, who seems a switched-on sort of guy.'

We would only use "switched-on" for things, not for people. For example, we might say "the phone is switched-on" or "the lights are switched-on." I hope that helps, Yusuke.