[ars]

That product is just two cables stuck together. Instead you could just simply run both types of cable to the doorbell, especially since they'll probably go to different places.

I googled a bit and it seems you might be able to run low speed Ethernet over untwisted wires if they are not long.

[jlgaddis]

10BASE-T1{S,L} [0] are "only" 10 Mbps but they also need only a single pair of wires (with the latter working up to 1 km).

They aren't exactly in widespread usage yet, though.

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(ETA: And apparently there are even 100 and 1000 Mbps variants now too [0] -- with lower maximum distances, of course.)

[0]: https://en.m.wikipedia.org/wiki/Ethernet_over_twisted_pair#S...