EDIT - I should have read the article, sounds like the child was not only not asleep but in pretty bad condition.
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It doesn't say if the 2-year-old was asleep (does it? skimmed the article) - if it was asleep in a crib then it was probably in very little danger. When we lived in an apartment we would sometimes put the baby down and when we were sure he was asleep we'd go to the apartment hot tub. The hot tub was right under our room, we could see our front entryway and the baby's window. We would also start a phone call and leave one phone in the baby's room and take the other with us on mute as a longer distance baby-monitor. I don't think this was putting our son in danger.