The first question in the series, with more explanation, is here
The model in question uses probability distributions over seven input parameters.
In this case we will be addressing the sixth parameter in the Drake's Equation, .
It is the fraction of civilizations that develop a technology that releases detectable signs of their existence into space.
Anything that would produce an unambiguous resolution that a planet bears intelligent life suffices. Radio signals are the technology that most suspect will bring about that resolution, but laser light, physical relics, and even gravitational waves can be considered.
Given our definition of intelligences as having both tool use and language, it seems unlikely that this parameter should be miniscule; nonetheless we give a range extending down to , open at the bottom, to be safe.
The resolution to this question will be the scientific consensus 100 years from now, regardless of any remaining uncertainty.