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Comment by _hijk | Hacker News Reader

Someone checks the eruv every week before Shabbat[1] and they have a weekly announcement if it is operational [2].

[1] https://www.npr.org/2019/05/13/721551785/a-fishing-line-enci... [2] https://twitter.com/ManhattanEruv/status/1388202630048993281

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Why not make it conductive and test if any section is down by seeing that the circuit is broken?

Wouldn't that mean operating an electric device?

You could check the connection before the Sabbath, similar to how you check the eruv integrity before the Sabbath. So it'd be fine. It's an interesting idea!

This is a fascinating idea and not something I've ever heard brought up. Do you think the authorities would allow a length of wire with a current passing through it to be erected in their city?

Aren't there millions of cables throughout Manhattan already, whether to carry power, telephone signals, etc.? The wire could be insulated and low-voltage, you know.

If I recall my electronics/telecommunications classes correctly, you would only need very little current. You could also send short pulses and wait for the "echo" back to have a rough estimate of where the cable is broken.

The biggest issue I see is about the cable length: you would need to use high voltages to make up for the losses and fault location would become way more difficult. Another option would be break up the cable in smaller sections and monitor each of these independently, but I don't know if that's a valid option for this use case since the entire point of the eruv is that it must be continuous (maybe the sections could be tied together using non-conductive materials?)

If you're allowed to step on an automatic elevator, you probably also are allowed to look at an LED and take action when it's off.

That’s what I do t get. Just because you’re not pushing the buttons doesn’t mean you’re not operating it... you’re still using it, and the end result is the same. The elevators still probably have safety sensors, so you’re still triggering them when you walk through the doors. What’s the difference between walking though a sensor and pushing a button?

It's like the Sabbath mode on some ovens that let you change the temp, but don't feed back the change to the display panel till after a random delay.

I guess if you add a Rube Goldberg machine to your electronics, it's ok.

My favorite was when I visited some family members that lived in a area with many devout Jewish people. The building they lived in didn't have elevators with a Sabbath mode, and when I entered the elevator, an elderly woman who had been waiting entered with me and mumbled "I live on floor 12". I pressed the button for her, but it was only later that I realized she was waiting for someone to do the work for her without specifically instructing them to do the work because of the day. So odd.

Because the eruv doesn't just consist of one single unbroken wire. It also often includes natural boundaries like rivers, but also other ones like fences, bridges and motorways. Often eruvim (plural of eruv) will be built with an irregular shape specifically so they can take advantage of these; thereby reducing the need for new construction.

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