Active 3D required an emitter that synced glasses to the TV's output, and the glasses themselves.
I assume passive 3D required some hardware to support it too, and both required hardware with firmware that could support the formats and settings required
It requires a polarizing filter/film that's aligned with the screens dot matrix.
In theory that could also be added as aftermarket modification.
If the screen is fed with an interlaced 3d stream and the screen firmware/hardware allows 1:1 pixel playback it doesn't need to know if the content is 3d or not.
I was aware of passive 3D being done with aftermarket filters (mostly as a joke, printed on laminate), but proper consumer 3D had to support the same formats that Active 3D did, which usually meant side-by-side and top-bottom
I assume passive 3D required some hardware to support it too, and both required hardware with firmware that could support the formats and settings required