Given that the original freakout on the part of the English teacher was precipitated by the alarm going off while the clock was in his bag, I'm thinking it was battery-powered, not plugged in. Power cords are cheap, easily accessible wire that are not necessarily always carrying grid voltage. Although that picture certainly shows a plug, so who knows? I do wonder how the alarm went off - if that isn't just embellishment after the fact.

That said, I certainly fooled around with live power when I was his age. The house didn't burn down because we had a competent electrician install circuit breakers when we built it.