There is no power or polarity or ground in the diagram, so (as is shown in several of the related "talk" pages, this diagram needs an update before being actually useful.

Drawing has a ground and is complete. The transistor is NPN so the circuit “sinks” to ground. The output would likely be connected to a sourcing input that provides the power to the sensing circuit. As discussed in the article, it could have trouble “starting” but should run fine.

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