"Is it plugged in?"
Translation:Onko se seinässä?
Since 'seinä' means wall, in this context, I'd assume that it means 'being plugged into a wall outlet/electrical socket'. What about other cases, in which, the action of plugging doesn't involve any wall? Like 'plugging a headphone to a phone' or what if the electrical socket is outside the wall (like 'jatkojohto'). Do we still use 'seinässä'?
You can say "Onko se kytketty(nä)?" or "Onko se kiinni?" both meaning "Is it connected?"
And after "kiinni" you can add the object you're talking about, e.g. the phone, the same way as you'd ask about the wall too: "Ovatko kuulokkeet kiinni (puhelimessa)?" (Are the headphones plugged to the phone?)
Or if it's a jatkojohto, then just ask if it's "kiinni jatkojohdossa".