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Comment by alias_neo | Hacker News Reader

I made something similar a few years back with a Pi 1 and a GSM "hat".

It came with a C SDK so I had to write AT commands to communicate directly with the modem and it worked great until I didn't need it anymore.

Its purpose was to text me when my power or internet connection went down at home then I could respond with commands such as to shutdown the servers etc.

When power/network came back it would text me the new address so I wouldnt need an outside service for DDNS.

The biggest challenge with the whole setup was finding a SIM from a provider who would let me top it up once per year and maybe send half a dozen texts in that time without deactivating the SIM, for a reasonable price.

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The plans obviously exist at least at the wholesale level.

These: https://shop.blues.io/collections/development-kits/products/...

Come with pre paid 10 year internet data plans - but with a 500MB data limit (which you can top up), all for $79 including the hardware and interface board.

In raw bytes, that'd be enough to send 1000 140character SMS messages a day every day for 10 years. Realistically, there's probably a 10x or 100x overhead for the TCP/SSL/transport/application layers, but you'd probably still get al least 10 140byte payloads a day for a decade with one of those.

(Full disclosure, I have no affiliation with Bluers.io, but I did impulse buy one of those when they first appeared on my radar, which is sitting in the huge pile in my Box Of Unstarted Projects And Broken Dreams.)

Thanks! Now I have a Good Name[tm] for my "junk" box(es). :-)

> The biggest challenge with the whole setup was finding a SIM from a provider who would let me top it up once per year and maybe send half a dozen texts in that time without deactivating the SIM, for a reasonable price

Good point - so-called "pre-paid" SIMs seem to be hidden subscriptions nowadays. Does anyone have a table of suitable low-usage, long-term SIM vendors?

You might want to say what location you are in for a truly useful answer.

In the UK at least most providers keep the SIM active if it sees some activity in a given space of time¹ irrespective of top-up activity². So if “low” use stretches as far as one text every month or two maybe just have it send an “I'm still here” message regularly. Also acts as a double-check that not getting alerts means all is OK instead of that the alerting service is broken.

1: the GiffGaff one I used for pure data for a week-and-a-half when my landline was down in2020, shut off after three months and a few nagging texts IIRC

2: though if you don't top-up once per month you usually drop onto the basic tariff, so no more “unlimited texts”, but if you are topping up that infrequently that is probably fine

What would be the answer in the US?

https://www.twilio.com/iot/super-sim-card is one example.

Search for “US M2M SIM” for more vendors.

Looking at B2B IoT services is one way to find prepaid SIM plans that don't require monthly top-ups, but usually you have to buy 5+ SIMs so it doesn't necessarily fit the single-device use-case...

Instead of paying for a separate SIM, I've been piggybacking on the "data only" SIMs that Google Fi let's you add to a normal subscription. No extra per-SIM fees, and you just pay for whatever data it uses at $10/gb.

More details on my modem, monitoring setup, and IPMI backhaul strategy using Wireguard here: http://jsharkey.org/ipmi/

That sounds like a nice idea. Unfortunately I don't believe anything similar exists here in the UK.

I can pay my mobile provider an extra £7.50 per month for a "second SIM" to share the allowance from my main SIM (you're effectively paying to rent another number).

It's not a terrible expense, but for something I need to send an SMS maybe 1 per quarter is a little much. I guess if you look at it as a "service" it's not bad, but this was a home thing, nothing critical would be lost if I couldn't get my home IP until I got home. Now I use DDNS using a small piece of Go code I wrote to update the domain on my Digital Ocean account as a form of "free" DDNS, it runs on my router on connect/reboot.

It surprises me how many people are willing to let Google know their home address.

You don't need Google Fi for Google to know your home address. An Android phone will do that. Or Chrome. Or really just broadcasting wifi. Really the problem is you have a home address and someone will sell it to Google.

I like what you did there. Google is a given, a person having a home address is the problem, the collection method is a variable solution.

They already know.

I like the country wide LoRa networks that are coming up helping with this purpose, all you need is like 1kb per month lol

A good free way to achieve this is to use Signal. This project https://github.com/AsamK/signal-cli enables you to send Signal messages from the command line, including from Raspberry Pis. It obviously needs an internet connection to work, but has the added bonus of being more secure than SMS.

Neat tech, but probably not super appropriate for this person's particular application, which involved detecting network outages.

I'm guessing if that USB Modem can send SMS, it can almost certainly also get a TCP connection. (It is probably easier to find a sensibly priced SIM/plan that lets you sand a handful of SMS messages a year compared to one with a ultra low data usage internet connection though.)

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