POCSAG Pinephone Hardware Add-On; Radio Silence, Privacy, Anonymity,and Freedom

[biketool]

Several years ago(2013ish) when the (folded project)Neo900 http://neo900.org/ was taking shape I requested hardware switches on all radio transmitters and a POCSAG pager module on the board.  The desire for an optional rx only radio silent un-trackable phone mode evolved into the Neo900's hacker interface where a developmental POCSAG pager module could connect in the future once the phone was available.  I had a few interactions with RMS and had an email thread with him where even the 'man who would not own a cell phone' admitted that if his conditions were met he might consider such a phone as his first mobile device.

The head of the Neo900 project, JoergRW, who's work you all probably know from the OpenMokos many of us have played with, sadly ran out of health and had to fold the ambitious project.

I want to see what can be done to get a POCSAG pager module and required software working with my pinephone.

The idea is that POCSAG paging service is still reasonably universal for medical and emergency services and is broadcast from FM broadcast, 400mhz, or 900mhz towers, these pages are passively received by the pager receiver.  If using a dedicated chip we were already getting 30 days or more form a AA alkaline cell so power budget is minuscule I believe most hardware comms are simple serial.

Use case:
If I were to soft deactivate my telephony modem I could be radio silent and untrackable, should I be in what I consider a safe location and wish to make a call it is simple for me to automatically soft activate my modem as part of the dialing process script and also soft deactivate when I complete my call.  More interesting to us all is that as long as I have a subscription to a paging service I can also receive calls under most conditions, often with better coverage than some mobile telephony providers, by receiving a page with a caller-ID which can be called back quickly with an answer button in the paging rx app.  The paging service can also often receive SMS and emails forwarding them to the user, with some middleware these could even be encrypted and decrypted at the phone removing another privacy invasion.
The always on nature of a mobile telephony device is used to track our every move, I want us here to break this cycle.

I believe that one-way paging, wireless peer-to-peer fidonet-like programs like Briar, consideration of integrated or tethered UHF radio tx/rx for amateur radio or unlicensed bands, and perhaps even use of fixed or mobile one/two way satellite data services can free us from many of the tracking and anti-user technologies which have grown up with cellular and internet technologies since the 90s.

[biketool]

For example a S-7040D can do all of the decoding internally and output serial, it is a very cheap 1cm IC and just needs a receiver chip a serial line, clock, and power, the 'ROM' line could be from the phone or a real ROM on the module.
http://www.sih.com.hk/sih_eng/products/i...040d_e.pdf
All that is really required is a RF rx circuit, for testing possibly a FM radio IC and antenna.
There are several amateur radio projects to do POCSAG paging under US and European amateur radio rules, a SDR with a 50ohm load could also be used in close proximity or over a cable with an inline atteunator to the receiver to send legally low unlicensed signals sufficient to activate the pager circuit.
Put the receiver on a flexible kapton PCB with the radio IC and connect the serial lines and we can get to writing the silent mode callback/answer software.
(as an aside using RTL-SDR for always on paging rx, or most other mobile power budget applications is not a useful direction as that chip is notoriously power hungry)

[tllim]

For example a S-7040D can do all of the decoding internally and output serial, it is a very cheap 1cm IC and just needs a receiver chip a serial line, clock, and power, the 'ROM' line could be from the phone or a real ROM on the module.
http://www.sih.com.hk/sih_eng/products/i...040d_e.pdf
All that is really required is a RF rx circuit, for testing possibly a FM radio IC and antenna.
There are several amateur radio projects to do POCSAG paging under US and European amateur radio rules, a SDR with a 50ohm load could also be used in close proximity or over a cable with an inline atteunator to the receiver to send legally low unlicensed signals sufficient to activate the pager circuit.
Put the receiver on a flexible kapton PCB with the radio IC and connect the serial lines and we can get to writing the silent mode callback/answer software.
(as an aside using RTL-SDR for always on paging rx, or most other mobile power budget applications is not a useful direction as that chip is notoriously power hungry)

You can design a small piggyback board using a microcontroller to control pager chip and communicate with PinePhone thru pogo pin i2c communication. The modem can be hardware disable thru dip switch or you can have write a program disable the modem and acrtivate when plan to use. For sure the program need to factor in the model initialization sequence and works with phone manager driver.

[bcnaz]

This 'may require' a separate carrier service to implement...?

[biketool]

This 'may require' a separate carrier service to implement...?

Yes, a paging service account and phone number would be required. There are still nationwide paging networks and the service is very common for first responders and medical/hospital workers.

Would you pay $10/month+a pager module for radio silence until you feel safe to raise your antenna mast like a nuclear submarine on patrol and initiate an outbound call, especially if you can still know what is happening while still not giving up your position to both corporations and the state security apparatus.
https://en.wikipedia.org/wiki/POCSAG

There are occasionally news stories of innocent people becoming suspects in crimes even convicted because the state has no other suspects but their mobile device was detected, triangulated, and logged near the time and place of violent or property crimes. Often these methods are hidden by creating a chain of evidence based upon choosing a preferred suspect and working from there.

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You can design a small piggyback board using a microcontroller to control pager chip and communicate with PinePhone thru pogo pin i2c communication. The modem can be hardware disable thru dip switch or you can have write a program disable the modem and acrtivate when plan to use. For sure the program need to factor in the model initialization sequence and works with phone manager driver.

If I can, I hope to lay everything out on kicad then use it as a guide to lay out and connect everything with magnet wire and sandwich that between two strips of kapton tape. It is super sketchy but I have no way to make a PCB that fine and dont want to order out for several revs. It will be wonky as I will be using through hole components for pull up/downs and coupling/decoupling for SM ICs, an attiny should be enough to control that Seiko receiver chip.
But first I/we need to get a breadboard test rig assembled and get access to a SDR though I think this could be done with a sound card audio and transmitter, maybe just mix and feed that to the Seiko POCSAG chip's IF in pin and skip the radio RX stage for breadboarding.

I used to have a DOS POCSAG encoder program though not the source, does anyone know of a FOSS POCSAG encoder for Linux? I recall a pre-built amateur radio repeater add on image for OrangePI and other cheap ARM boards a few months ago that included the encoder for amateur radio paging but I didn't find source for it.

[jmorris]

This 'may require' a separate carrier service to implement...?

It would.  You would have your normal cell carrier and service from a paging company.  You would have your cell carrier set to forward all incoming calls to the paging company or if they support it, just forward calls when your phone is out of range, which is what it would look like to them when the modem was powered down.

If this became popular, i.e. adopted by a major phone hardware maker, cell companies would sign agreements with paging companies and bundle it on "privacy enhanced" service plans with different levels of paging service (local, regional, national) included.  Done right your phone could know the paging coverage map and switch between paging and normal cell service as needed.

The primary reason this doesn't exist is the cell carriers saw no demand for it and lots of profitable upside from LoJacking every customer.  We have to push back, reclaim our privacy.  In reality, if there were demand or government pressure, the cell towers themselves could probably do this.  Just broadcasting "paging" signal across all the towers in an area wouldn't suck up too much of their total bandwidth.  Given a choice between that or paying a fee to a paging company, there would only need to be a couple percent of customers willing to pay a premium to make them modify the cell standards to capture that revenue stream.

[biketool]

If this became popular, i.e. adopted by a major phone hardware maker, cell companies would sign agreements with paging companies and bundle it on "privacy enhanced" service plans with different levels of paging service (local, regional, national) included.  Done right your phone could know the paging coverage map and switch between paging and normal cell service as needed.

Back in the 90s there would be a few towers and east/west and all of US plans, the coverage was way better than cellular, it only took a few towers per urban area or highway stretch, think FM radio broadcast coverage good. Paging became super cheap by the 2000s, they even had free service if you would accept a few dozen spam pages a month; voicemail all as well as email to page gateways; you just email your pager number ie 5551212@thepagercompany.com. For a while back then I had no $ for mobile phone service so I used my pager for incoming calls and called back on my amateur radio club's repeater telephone autopatch. Only downside is everyone using the repeater got to hear my phone calls or voicemails if I couldn't find a payphone or landline to call back on.
_______________________
Anyways the way I imagined it the incoming page GUI would look like an incoming call or SMS and throw the notification that could be used for a smartwatch or whatever else needs that, maybe with a colored border or something so we knew the phone was safely offline. and instead of an answer button a safety yellow and black striped online and callback button maybe even with an are you sure dialog.
Whatever service used it would need an option to automatically send a caller ID if you phone was called directly but was offline so went to fallback number(this is in many cell carrier settings) but also forward SMSs when offline which is uncommon AFAIK.
A really good paging service with cellular bundle might need to be negotiated somewhere as a test market, possibly not the US/Canada where mobile telephony is an insane monopolistic mess but a smaller more open market somewhere like Eastern Europe or Asia.

here is one example, it requires a US ip address to read but starts around $16-24/mo for text paging cheaper of only numeric service. interesting that it CCs alphanumeric messages to your phone's SMS.
https://pager99.com/rates-99

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This is a pretty good answer from one pager company.
From the pager99 faqlinked above)

Why are millions of pagers still in use in 2020?

After all, doesn't everyone just use a cell phone with text messaging?

We've seen the articles declaring the death of the pager and we hear it all day long..

"Do they still make those things"?, "Pagers are old school", "What's that???!!!!" "I haven't seen one of those since the 90's!", and last but not least..."Why would anyone use a pager when they can have a cell phone"?

With millions of pagers in use today, Let us be the first to tell you that pagers are not only alive and well, but are THE backup communication source relied upon by people who absolutely have to be accessible.

Pagers provide an easy, inexpensive and reliable way to stay in touch. The main reason pagers have stood the test of time is because they provide privacy and urgency over and above what a cell phone by itself can provide.

Pagers are more reliable and much less expensive. While we would never say a pager is a substitute for a cellphone, just as a motorcycle is not a substitute for a car....Pagers have their place as a dependable wireless communication tool and when used in conjunction with a cell phone, you will not only have a backup communication tool, but you will also have piece of mind.

Paging is speedy and reliable, it is cost effective, it has excellent coverage and building penetration, it is simple, it rarely suffers from congestion, recent events have shown that it works even in times of disaster as opposed to cellphones, and it has a unique facility in Group Calling where large numbers of pagers can be paged simultaneously.

Not everyone is so important that they need backup communication, but when your burglar alarm goes off or your patient needs you or your kids need a ride home and your cellphone is in a dead spot, keep in mind that for under $9/month...you too can have an alternative communication solution for the people who rely upon you as opposed to just not getting the call in time and missing out.

[biketool]

So prototyping; I have a (hopefully) temporary medical condition which makes me unable to work with these small SM components for now. Someone with a supply of passive components and some soldering skill should be able to lay this out on a PCB or even stick the IC to kapton tape and solder required pins with magnet wire to breadboard the seiko pager IC for about $5-10 with several spare ICs.
It should be possible to feed the chip with soundcard audio of the POCSAG signal, even playing a mp3 of the audio should be fine.
Alternatively we could use a fully functioning pager and just tap the serial line comms though that would likely require a SDR or amateur radio transmitter and a pager tuned to amateur frequencies.
POCSAG information and MP3s for testing
https://www.sigidwiki.com/wiki/POCSAG
The starter app could be a bash script which greps the different parts of the serial output and turns it into a click to modem power-up and dial a dial-able phone number and/or display a SMS like text message.
edit(sorry stuck using low speed mobile data for a few months)
encoders galore including for gnuradio
https://github.com/jjwbruijn/POCSAG-Encoder
https://github.com/faithanalog/pocsag-encoder
http://hilftvorne.fun/on1arf/gr-pocsagt8wo1580hb6s
https://github.com/unsynchronized/gr-mixalot
this is an alternate IC form Motorola controlled by an ATmega
https://github.com/jp112sdl/arduino-pocsag

[biketool]

I suppose I need to gauge interest in the project and if there is interest in me figuring out a dev kit.
I hope that there is because while there is utility in the hardware and software radio switches(I love that you thought to put them on the mic and cams too!),
I feel like without any way to be contacted the switches have few cases of practical utility beyond novelty for most users, when Neo900 team came up with the idea the POCSAG receiver came first and then the hardware/software RF switch idea second because we didn't trust the black box modem modules to assuredly shut off.

There would be three types of kit:
1 - an initially kapton tape and magnet wire POCSAG decoder chip wired with all required pullups/downs and (probably wont need)band passes, probably needs processor and/or rom ICs, with lines for power in, data in, and serial or i2c data out lines though if there is interest the pinephone hardware devs can probably guide us to a good PCB setup, call this about $5 if we do at least 5-10 sets and some SM pin soldering if we DIY it on Kapton tape.
2- same as #1 but with a full function radio receiver chip too, this would be a fully functional breadboard setup and would require #3, a POCSAG paging subscription, or another way to send test pager signals, $10?
3- #2 kit with a cheap low power transmitter to use for reference alphanumeric pagers and the pinephone pager module, I recommend the very inexpensive RFM69 module which in the post above there is Arduino code and schematic to run this as a POCSAG encoder/transmitter $15 for the functional receiver and RFM69 transmitter module, the RFM69 will need an arduino or ATmega32 to control the RFM69 but an Arduino can be found in educational supply shops, even toy stores if you don't want to order one.

4- An ordinary commercial pager would probably be useful reference for devs, I think the Apollo 924 UHF pager(they have low and high VHF and low and high UHF pagers so whatever is useful with the commercial paging service or amateur radio paging rules locally), is pretty cool as it can be hand programmed for both pager ID# and frequency including 433mhz where that is unlicensed or on amateur bands if you are not in a country which still has POCSAG paging subscriptions available. I got one for $20 a few months ago. https://www.apollopagers.com/wp-content/...Manual.pdf

With a transmitter you could at least enjoy the radio silence mode at places in range of where you can build a pager station, if you are an amateur radio user you can put up a tower or strap a mast to your house and cover maybe a few km with permission maybe even use a repeater in your city and cover thousands of square km, at unlicensed micro power you could have a micro station at work and home maybe tied into your landlines caller id, have one installed wherever you spend time, you could even put a module in your car and at least give you a footprint of minimal privacy when you go pedestrian, amateur radio license holders could put a good UHF antenna and receiver in their car and and set up a mobile repeater for signals from the home or amateur radio club pager station, you could even filter the repeater to only pass DIY transmitter or commercial signals with your pager id#.

FYI most people who can solder should be able to assemble from schematic if we decide on a favorite dev kit layout. Where I live postal service is very slow and will probably need to be forwarded to someone to remail as international postal rates are high; also I will probably not be able to do SM soldering for a few months. I plan to use kicad once I have time to sit down and to do schematics and wiring layouts as kicad can also export gerber files which can be sent out for PCB makers later. This will all be low budget DIY friendly with minimal tools and cheap auction site parts as I currently do not have access to proper facilities even my internet is a very slow mobile phone bridge, thanks COVID-19! If anyone has input please let me know.

Also also...
If there is interest I will try to dig up my(edited for privacy/brevity) email thread from years back with Richard Stallman where I get feedback and exchange ideas on a post N900 community designed FOSS ready pager/switches phone, he still wont own a mobile phone.

[notpod]

HAM RADIO guy here. I like what I read, Will think about this some more. And we have LoRa options now...