[fyfy18]

This is how Power Nap works. Even though the lid is closed and your laptop is supposedly asleep (on battery or AC), the software can still wake it occasionally.

https://support.apple.com/en-us/HT204032

[Godel_unicode]

Siphoning power from a data connection is sci-fi and not at all how Power Nap works. It's just a fancy sleep mode plus a timer.

[im3w1l]

I don't know what you mean by sci fi?

Consider this sensor https://martybugs.net/electronics/tempsensor/hardware.cgi

If someone used such a sensor and overlooked the parasitic mode, then that could be used even when the power was physically shut off.

[Godel_unicode]

You appear to be suggesting that a temperature sensor and a MacBook in Power Nap mode use similar amounts of power. That is not the case.

Even in the webcam case, powering the camera CCD would take significantly more power than is supplied by the data line. You can derive this for yourself without taking one apart by realizing that the power is supplied separately for a reason.

Further, it's not the case that this would work when the power is "physically shut off". If there's no power then there's no power.