That _is_ an interesting question. If there is an eruv, carrying is fine. Motion sensors are _not_ kosher as I understand it, so I think this idea wouldn’t fly either.
Such a company is not entirely unimaginable given sufficiently roundabout sensing mechanisms. It could be especially useful in Israel due to the majority of the population being Jewish and with many neighborhoods and towns nearing 100% Jewish residents. Mostly, though, religious Jews in Israel are just used to not having a Shabbos goy as an option. That said, the one time I found myself really stuck in a bind where a Shabbos goy was the only reasonable solution, I was fortunate enough to see a non-Jewish taxi driver pull over within minutes of going outside to look for one.
Contrast that with a device that constantly scans for faces and is continuously sending instructions to the elevator controller. In this case, it is always sending an instruction about which floor to go to. If no one is present (and nothing is happening on other floors), the instruction is to stay on the current floor, doors open. If someone approaches and is not recognized, then on the Sabbath the instruction would be to go floor by floor. And if someone approaches and is recognized, the instruction would be to go to that person's floor. In any of the three cases, instructions are being sent via continuously-active circuitry. This is different from the motion sensor, where a circuit is completed only when someone is present and triggers it.
But like I said, I know little of this subject, and I'm sure these ideas have been vigorously debated by experts!