Actually, there are units similar to this that update over Infrared (even non-directionally)

Best Buy use them as price tags: https://www.youtube.com/watch?v=7aVoeDC-7MA

Similar insofar as using e-ink, but they're battery operated (from what I can tell). The "coolness" of what I'm talking about would come from being a completely passively-powered device.

The power density of light is vastly higher than the power density of Wi-Fi almost anywhere. If you can't do it with PV, you definitely can't do it with Wi-Fi.

WiFi -> electric current rectennas announced a year ago[1] were in the range of 40 microwatts, and the blog post says this NFC system runs at 1.4 Watts, that feels a long way away. But years ago LCD calculators could run on a solar cell the size of a finger and powered by ambient room lighting - surely must be some close to crossover level available.

[1] http://news.mit.edu/2019/converting-wi-fi-signals-electricit...

I'm wondering if that was a constant 40 microwatts, and if that could be stored in capacitors so that every 4-5 seconds (the refresh rate of the panel) there would be enough energy accumulated to power the circuitry for an update.

Yes is the answer, but it would be much slower. Assuming 1w for 6 seconds (4s refresh + 2s transfer), it would take about 42 hours for a lossless storage + regulator circuit. 40uw is an incredibly small amount of power.

It doesn't say that the e-Paper requires 1.4 Watts. The board that can be used as an alternative to a mobile device provides 1.4 Watts.

Interesting thought. At that point (or for that fact - at this point) it's is essentially a reusable printable paper. For people arguing about the low resolution of the $70~ model, I would not disregard their argument because we haven't seen it in real life and would love to see how documents scale up on that display.

If you aren't using super-white printer paper, not sure that this is any more eco friendly than printing a sheet of paper off twice a day, every weekday for years. Not sure what the materials impact is for e-ink, and paper is a renewable resource and sourced from trees generally grown specifically making paper as a crop.

We already power our iPads via POE< which is also how you'd power those beacons, so it's not really a great improvement.

BUT the idea that you would "tap in" to book it would be great.

I'm talking about radio energy powering the device. 802.1 beacon radio frames, which your access points send out over the air. Configure it via USB, etc, then just hang it on the wall. No cables. Just a passive device.

Is there a PoE to lightning adapter?

edit: $28 splitter, https://www.poetexas.com/products/af-lightning

And $100 Belkin Ethernet-PoE adapter.

Use a PoE to USB (female USB-A or USB-C) adapter - variety of models e.g. I saw one for $10 on Alibaba.