Your assuming the WiFi signals in homes now represent all the signals humans output, this isn't the case by far.

Not at all. We're still spewing out commercial radio, and TV. But we're slowly converting them from analog to digital, which uses much less power.

An encoded signal still appears as a manmade signal and not the result of a natural phenomenon.

Many of our digital signals are spread spectrum, hopping across a wider spectrum than analog. Distinguishing our own frequency hopping signals from noise is difficult, and an active area of research. If aliens use a similar technology, it seems unlikely that we would notice them.

Even if they used lasers, that would make detection easier. Lasers are not a natural phenomenon. If we observed one in nature that would be a new mechanism or evidence of alien life.

The sky is huge. It seems highly unlikely that we would happen to have a compatible detector pointed in the right direction at the right time. Even if we did, the signal would probably be compressed (meaning that its modulation would look like noise) and the lowest possible output, meaning it would probably blend into the background.