Zyklon B was not developed for killing people. The most common usage was for killing lice in clothes. (To make it very clear: It was also used for killing people in Vernichtungslagern).

Just spoke with a tour guide about this topic. If you lived in a city during the middle age in Europe, the night watch announced the current time every hour. How did they know the time? They just guessed, because nobody in the city could know better.