"First, there is a purpose. Which is to stop living organisms from committing murder. Two, murder may be defined as an act of violence, consisting of breaking, mangling, maltreating or otherwise stopping the functions of a living organism by a living organism. Three, most murderers are detectable by certain chemical and electrical changes."
Macintyre paused to light another cigarette. "Those conditions take care of the routine functions. Then, for the learning circuits, there are two more conditions. Four, there are some living organisms who commit murder without the signs mentioned in three. Five, these can be detected by data applicable to condition two."
"I see," Gelsen said.
"You realize how foolproof it is?"
"I suppose so." Gelsen hesitated a moment. "I guess that's all."
"Right," the engineer said, and left.
Gelsen thought for a few moments. There couldn't be anything wrong with the watchbirds.
"Send in the reports," he said into the intercom.
High above the lighted buildings of the city, the watchbird soared. It was dark, but in the distance the watchbird could see another, and another beyond that. For this was a large city.