Building a tiny paging network - EMF 2026

Hey everyone. Um, my name is Sam Hin. I'm going to talk about paging. Um, something that got incredibly out of hand for me this year in the best traditions of EMF. Um, this started off um, if Marcus in the room somewhere, there was a conversation with Marcus on Fetty one Januaryish weekend about, oh, wouldn't pages be really cool for on call? And then it's like, you could probably make that stuff work. And it, yeah, snowballed from there. So um this is a bit of history of paging um and also how I've built the world's smallest pager network. Um so I say we're going to we're going to talk about a bit about the concept why I think actually think paging is quite good and what's different about it some of the history bit of today and we'll try and do some demos if uh everything breaks. So what is kind of what what is um I can't really see but probably quick show hands any people in the audience that are over I'm going age now 40 probably will remember the ' 90s and pages and stuff people that are under about 25 are probably like what's a pager um so it's definitely an ask your ask your dad kids um pager is a small receive only and that's an important factor wearable device that alerts its user this This is what we used before mobile phones. Um, pager networks use broadcast radio. So whereas your mobile phone is talking to your local cell tower and it's a transmitter and a receiver and you've got to have coverage, paging networks are far more like broadcast FM radio, you know, like radio one or something. It's a big powerful transmitter on a hilltop site that just blats out a signal. And the pages themselves are just receivers. They do not track connect to the network. They do not talk back. Um, all of those hilltop sites are then usually connected via back hall. Ironically, when the networks were in mo most commonly, and I think the one network that's still running today, it actually uses satellite for the back hole. So, the message is sent up to a satellite down to probably about 80 to 100 paging sites around the UK. You'll get full UK coverage with in the order of 100 base stations um over a satellite and then broadcast out from all of those. Um, most pager networks or the public paging networks are then linked to the phone system. So the way you send a message to a pager is the pager has a phone number, you call the number, you speak to an operator, human being, you have a conversation with a person, which is a bit, you know, strange for some people. Um, you tell them the message, they type it into the computer and hit send and it comes up as on the user's device. Um, so what's what's good about pages? Firstly, it's a dedicated device. Like your phone is information overload. You've got 101 notifications. You're getting pop-ups from T-Mu to buy something for this day. You've got WhatsApp. You've got Signal. You've got Facebook. You've got all this stuff on your phone. So if it's something important, if you've got a particularly, you know, an on call type role, safety critical, emergency call outs, all this kind of stuff, putting that into your phone can sometimes mean like you have to therefore you have to then manage all the other notifications and put your phone into a mode so that yeah, I don't want like Facebook Messenger waking me up at 2 in the morning, but if somebody's dying, I want to be woken up at 2 in the morning. So the dedicated bit of hardware that you can put by the bed and switch the phone onto silent has an advantage for that. It's much more usable. Um it's a receive only device as I said and that's that's quite useful because the battery in these things will typically last 6 weeks not you know 16 hours like your phone. You just put a AAA battery in and and it sits there and and lasts for ages. Um it uses a low frequency 150 MHz VHF. So again, like you don't have these kind of shadows of coverage and oh it doesn't work in my downstairs dining room. Pretty much, you know, the signal will get through. Um better battery life, better coverage. And also they're unttrackable. Um people might remember a few years ago the Hezbollah Mossad pager thing. Whenever I talk about pages, oh you blowing someone up. There was a whole thing Israeli intelligence put some compromised devices into um the supply chain that Hezbollah leaders were then ended up carrying and then they managed to blow them up. The issue was why were in 2023 you know Hezbollah still using pages and this isn't because it's an old you know they're stuck in stuck in things. It's because a pager is receive only device your phone the network and anybody that has access to the network knows where your phone is at any one time. And if you're somebody that doesn't want somebody that can access the network, aka a nation state, to know where you are, carrying a pager means people can send you a message, but the network has no idea where that device is. So they're very good for untrackable. There were some other things in the '90s why certain other people quite liked carrying pages that you know their customers could get in contact with them, but they couldn't be tracked. Um, you know, and also alert, read, respond. Somebody phones you, you get phone call at 2 in the morning, you wake up, huh? What? And gives you this information. You've got to process it. Your pager goes off at 2 in the morning. You wake up. You wipe the eyes. You get your brain in gear for 30 seconds. You read the message. You call the person back. That's kind of, you know, a better user experience. Okay. Um, so on to the tech. There are two predominant standards in paging. One called Poxag. This was written in 1981. Um, this is the predominant paging standard still. um and and has been since since the early 80s. It's the post office council standards advisory group. So it tells you how old the telecoms is when this was written by post offices. Um again for those of you under about 40 50 um the post office used to run the one phone network in the UK. It was the go the general post office because you know when telecommunication telephones came out it was another form of communication and the people that ran the communication the government delivered the letters. Um so Post Office Council Advisory Group um the pages use what's called a Rick number RC radio identification code. Um not Rick rolling but um there it's also sometimes known as a CAP code. Cap code is like a Motorola specific terminology but Motorola made a lot of pages. Um it's a 21 bit number. So you've got about 2 million possible codes within your paging network. You can have two millionish unique devices. Um, so actually not particularly scalable, you know, by mobile phone standards. We've got somewhere around 80 million mobile phones in the UK. Um, modulation is very simple for for the radio nerds of us out there. It's uh two FSK frequency shift keying. So you've got a carrier wave and you just key the frequency up and down. Uh, a 4 and a half kHz frequency shift. Um, and then there's 512, 1200 or 2400 bps bits per second. So again really old modem standards like 56k was the last the fastest of the dialup modem. The fastest paging data se speed is 2.4k. So it is quite a slow data speed over the air. Um three different types of message in in poxag. You have what's called a tone only. So very basic pages that would just beep and you had no num no display nothing. But it was more you knew what that beep meant. It goes beep and you go you phone the office was the original one. Traveling salesman. and his little box in his b belt goes beep. He phones up the office and says, "Oh, have you got a message for me?" And very very analog numeric pages that could just send numerical messages. So maybe a phone number would come up. The first pager I had at 14 15 um was a numeric pager. Um and then full text so you can display a string of text a bit like a text message. In theory unlimited me, unlimited length of message. There's not been anything in the standard that defines message. In practice with airtime and stuff, you're probably talking about 90 100 characters um most of the network support. So little bit less but not a lot less than a text message. Um then we get on to flex slightly more modern um standard. This was created by Motorola um in the '90s. Um it's still, you know, using analog radio. It's still using um FSK. Um they did introduce four FSK modulation, so faster data rates. um 16 or 3200 bits per second um and can be used again really the same as proxy doesn't matter but I have seen pages that work on anything from 26 meghertz so kind of that's the old CB band like frequencies um often like hospital on-site ones things like that right up to in the US they actually ban paging at 900 meghertz which is like mobile phone frequencies and there's some crazy stuff in the US that I haven't mentioned again you've still got Rick numbers same space um the interesting thing with Flex is it's synchronized. So over the air, a POXAG transmitter doesn't send anything until it has a message. When there's a message to send, it just transmits, blasts out a a synchronization signal, a wake up signal. The pages will wake up. All the pages receive the message. They look at the the Rick number and work out if that's for them, and if not, they ignore it. If it is, they save it and bleep. Um, Flex, every 1.875 seconds, the base station sends a little burst. It's like a synchronization signal. Um, and the flex pages will synchronize. So, they're still receiving, but they will synchronize to that. So, when you first power it on, it takes a few cycles of, you know, a few seconds to actually synchronize up. And then the receiver in the page will only wake up every 1.8 seconds for well up to two seconds, I think, basically. So, 125 milliseconds of receive and then they'll go back to sleep. And apparently, this was more efficient. still sugar this guy but yeah it was an interesting thing when I started decoding these signals um there is something in in flex called the emergency resync signal so if you have a device that isn't synchronized you can wake up all the pages by sending a I think it's a 5-second long burst of data and any flex pager will just synchronize to that and receive a message um so the '9s um which was actually quite a long time ago I don't quite believe it yet but you I still feel like 1998 was like fairly recent. That was modern, wasn't it? Um, what was happening in the '90s? So, mobile phones, mobile phones were around in the '90s. Um, we didn't have prepaid until very late '90s at least. So, you had to have a contract. There was, well, there there was four networks for most of the '90s, but you still had to sign a contract. It was probably about 3040 a month. Um, and you know, calls were expensive. Um, and really mobile phones were not accessible to the masses, at least until the latter stage of the '9s. Um, the other thing that introduced paging that that really took off notes were what was called party pays, CPP pages. So again, pages has been around for a while, but you had a contract, you signed a contract, you paid a monthly subscription, £15 a month. They were very much a business type device. Um I think it was Page One were the first company that came out with this concept of CPP pages where you could go and buy a pager for 60 70. Um and that was it. There was no subscription but anybody that called your phone number for your pager paid 4050 p. So it was like a premium rate number. Um and that was what was great for kids and things. That was why I had my first one because you could buy it with your birthday money or it was that sort of price band. but then you didn't have a subscription, but when your parents wanted to get hold of you, they called you on the home landline. Um, and you just got charged to the home phone bill. Um, and as long as you didn't spend all your time calling your mates and running up huge phone bills, sending pager messages to your mates, then, uh, you didn't get in too much trouble. Um, and also the culture, it was kind of, you know, it was on all the kids TV shows, the teen stuff. Um, pages were coming out in like bright neon colors that, you know, this kind of design of the ' 90s that fitted really well with our shell suits and and that kind of thing. Um, I also found a fantastic source of reference for history of tech. There is a website that has every Argos catalog online as a PDF since like 1984. So you can and for again for those of you that age remember browsing the Argos catalog looking at all the cool toys. These are the pages from the Argos the pages of pages from the Argos catalog um in 9596 97. Um, so you can just about see the top one left there, first one, that was the one I had, that was a numeric only one. That one was $79.99 when it came out. Um, the other one below it was numeric. 96 I think we were still kind of the same. The prices were coming down a bit, but they were numeric. 97 was when text pages came out. So I upgraded to that far top green Vodafone Zap one. I had that one. Um, and I could get text messages and then you had an operator and things. Um, and there was a few different designs and you could start to see the colors coming through. Um, and then by 98 we see like prepaid mobile phones from Orange just started coming in. Um, pages were kind of this was sort of the dying end of pages. Um, really the late '9s as as prepaid mobile phones took over. But you had these colors. You actually had a flex one. That little far end light blue Motorola one um is a flex pager. Some little ones. they got kind of a bit less corporate, a bit more fashionable. This was fashion in the '90s. Um, but yeah, the Argos catalog is fantastic for this. So, where are we today? Um, pages are still in use today. Um, these photos are all well, I did a version of this talk back in March and as of mid-March, these were people, friends of mine's active pages. Um, that top green one, that's a hospital in Somerset. Um, that is an on-site paging system for the medical regge. So that is the device that is carried by the on call medical registar around the hospital and how they contact her on her shifts. Um that's one that just bleeps doesn't have a display. It does do voice and there's some interest voice paging I haven't looked into. Um it's an on-site network so they have a transmitter on the roof of the hospital. The pager only works around the site but obviously you're you know it's to call you from wherever you are at one end of the hospital to run to the other end of the hospital usually and then get you to run to the other end of the hospital. And the other um fire brigade. So again, friend of mine's a retained firefighter. Um that's his AAN fire brigade pager. So the fire brigade run that because if you're a retained fire crew, you sit at home, you know, you have a day job and then there's a fire, your pages go out, you run to the fire station, you get on the truck, you go. That's still how the fire service is done in, you know, outside of cities in a large part of the UK. Um fire service run their own pages, their own frequencies. That's why you'll quite often see on a on the tower, the training tower next to the fire station, there's an antenna on the top of that because that's their paging network. And again, because the people are local to the fire station, they only need to cover I think you have to be within 5 minutes of the fire station to get called out anyway. So if your pager is, you know, doesn't have coverage. It's no point paging you here to say, "Oh, there's a fire in Somerset. Can you please come and get on the engine?" Because, you know, you'll be long gone. So they they page everybody, wait till they get six people and go. Um, RNLI again another on call thing. They still run their own private national paging network. Um, so they have hilltop sites and um, again the local the crews all carry carry pages. And then there's crit as it's sorry crit crawl up there's critco um or what used to be known as page one. They rebranded. This is still the live UK public national network that's operational. So they have two frequencies um a flex and a poxag channel and they still have people with subscription pages. Certain organizations are still using them. Um there's some bird rescue stuff that I keep seeing. You can actually decode pager messages over the air and I keep seeing ones occurred corrant in this wildlife park or something. So there's some variation of like RSPB use page their paging network and a few other things. Um so on to demos. Let's see. We didn't have enough time. Um, I've, um, I say this all got a bit out of hand. Let's just get this. And I ended up buying a few old pages on eBay. Um, I had a bit of a habit. Is that showing? Oh, no. There we go. Uh, so yeah, this this this box was uh mostly empty at the start of the year. Um, I started buying up all the old pages I could find. Oh, there's some latency on that. Um, but there's a few interesting ones. Um, this one is a Cryco pager. Um, or a page one pager. This is a CPP pager from the '90s which has a phone number on it, but it's still live. So, this is was bought for 60 quid back in the '9s. Um, and the number most of them are disconnected because if you didn't receive a call for like 3 years, they disconnect it. Um, this one it turns out is still connected. Um, and so we can call >> the pager. >> Afternoon. Welcome to Critico. The new name for page one. >> Please hold the line for an operator or enter your numeric message now. Followed. >> I'll just put a numeric message in rather than >> Sorry, the message was not accepted. Thank you for calling. Goodbye. >> Demo fail. Um, it did work earlier, but basically, yeah, that would have cost me 75p. Um, there's a weird bug as well that it'll get refunded tomorrow by the phone operator, but yeah, that is still a live pager. Um, some of the other more interesting ones. Um, this is one of my, can I have say favorites? This is one of the nicest. Um, this is the Motorola Adviser, the one that's in hackers. So, the one that the serial killer uses that he spray painted neon yellow. It's basically one of these. Um, so this is not this is an XBT one. Um, BT's network is is dead. I don't know if you can see the screen too well on that. Let's just move down a bit. Um, turn the light back light on. There we go. Um, but yeah, so that's uh that's on there. So, the network's dead, but I discovered about building a tiny network. Um, you can build your own paging transmitter. Oh, I figured out how. So, has anybody seen one of these um Laura Tracker friends in the audience? This is a SenseCap T1000E. So, it's a Bluetooth device. It's got GPS in it, but it's also got a little radio in it um for Laura. That radio is actually incredibly programmable. Um so, that will go down to 150 MHz. Um this runs at 153 MHz. Um this will do FSK modulation. Poxag is FSK modulation. So, I have some custom firmware on here which will now act as a paging transmitter at incredibly low power. I've got it set. This will go up to about 22 dBm. Um, but you can go down to negative9. So that's like 0.01 mill. Um, but we can actually and just in case there's anybody from Ofcom in the audience, I have this lovely Faraday box here. Um, just to uh so I will shut the lid. But what I've then built is a little see my phone. Uh, yeah. Uh, so I have a a little iOS app which will connect to the device over Bluetooth. So I'm now connected to this on Bluetooth. Um, I've set the frequency. I've set the power. Uh, and I can 1442493. If I enter the Rick number of the pager that pager 1442493 and our message hack or hack the planet. That won't work. It's got to be correct. attack the planet. I'm just going to keep we'll try not to leak too much RF. I mean, this is incredibly low amounts of power, but technically it's a licensed band. So, and that's received the message. Um, so if we open it up, [applause] how do I turn on the back light? There we go. You can just about read it says hack the planet. Um, you can also, I don't know if you can see just on the screen down there, but it says the date uh 1st of Jan 91 because when I put a battery in, it reset to its default time. So, that tells you the kind of era it's from. Um, it's um that's that's a fairly old one. This was the oldest one I managed to find. Actually, this, as you can see, is the precursor um to that. It's the Motorola PMR 2000, which you can tell how old something is because they called it 2000 to sound futuristic. Um, but this is a a pre a pre- version of that. This I think was 1987 this design came out um similar to that but again really old. Um and yeah there's a whole bunch of stuff here. Um this again is another nice one. This is a a flex pager um made by BT. This is actually an Ericson flex pager. It's the only Ericson one I managed to find. But um and yeah, there's a whole load. Also uh Swatch watches. If anybody remembers Swatch watches from the '90s, they started making swatch watches with numeric pages built in. This actually has a pager inside it. um with a second battery and a phone number and it receives numeric pages so you could have a really stylish 90s watch. So we have time that's that's the most of the demos. Um the other thing I say you've done it with those little sense caps. I also if you've got the Hletech um radio boards this is one of those um Heltech V3s again I've put some custom firmware on it. Wi-Fi IP paging gateway so that you can make transmit to a pager. Um oops uh are we mirrored? No. Back to slides. Cool. Play slideshow. Perfect. So um like I say this got a bit out of hand. I started playing around. Hey, I can make old pages work. Um, I can transmit pages. I can also these can receive pages. Um, the RF is a bit harder on those because these are tuned to a very specific frequency. They're quite wide transmit narrow receive. Um, so these will only receive on the lower 868 frequencies by unless you're like right on top of it kind of thing. Um, but then I started thinking, well, there's another you can buy lower boards that also do like 400 to 500 meg. The Chinese lower frequencies are are down at the 433 band. Um, so but it's the same chip and the same firmware. Um, so I was like, I wonder if I could build something that that would run at 433 because that's a more usable frequency. Um, and so we ended up hold on camera. We've got it here. Um, I ended up building a expansion for the badge. Um, so this is Bleepy. Um, this is a poxag paging transmitter and receiver for the badge. Um, uh, so I built I've built 40 of these. Um, she'll talk about the end. But not only that, we also have a paging network on site because why not? Um, so I called it bleepy paging with some keynote designed artwork with um, and so around the site there are three I'm calling them digiper nodes. If you're an amateur radio person, APOS, Digi, same concept, but they're basically little Heltech boards. There's one in DK at the top, there's one just out here, and there's one at the far end of the site. Um, and those will receive messages, send and receive messages um, on the same frequency as the bleepy boards are set for. And then so you can transmit, you can write a message from your badge, send it, it'll be picked up by one of those digies and rebroadcast by the others. Or if you're close enough, badge to badge will also work simplex. You don't need the network. Um, everything runs on the same frequency. These just like they dig digital repeat. So they don't repeater in in an analog way, but they store and rescend. Um, so we put these up this morning and I don't know if you can just about make out from the map, which is satellite one because I couldn't load an EMF map, but this is the kind of coverage. So I had another app on my badge which has the GPS in it and I walked around and every 5 m it would page out my GPS coordinates and then the digies were picking that up, storing it, um, and plotting it on the map with the colors. The colored dots aren't great because I got the scaling a bit wrong. Actually, this is good signal. So red is neg 104, but it's still perfectly usable. Um, so you can just about see the really light areas when I was right close. I should have I should have scaled like neg 30 is green, neg 110 is red, and I I did a linear scale in between. But actually, um, you really want to be like neg, you know, neg 94 should still be green anyway. So most of that should be sort of green and yellow rather than yet red and orange. Um, but yeah, so we have an experimental paging network. Uh, it's on 433900. If you've got one of the uh programmable DANET pages that you can change frequency, you can also stick that on there. All of the bleeps will generate their own Rick number. Um you can also subscribe to other Ricks. What I didn't say about Rick, sorry, is paging has no concept of a from address. It has the Rick number and the message, but you don't know who it's from. There's no there's no from. There's only a two. Um, so when you're sending a message, it will literally you can just send it to a number, send it to a Rick and the page will receive it and they have no idea what sent it other than the network. Um, there's also a little voice AI paging viewer I've built. Um, so it goes to an anthropic LLM and some text to speech stuff. But if you call 25337 um, on the phone system, it'll then ask you to key in the pager number, the Rick number, and you'll speak to Anthropic and see if it can decipher what you want it to send. It'll pretend to be a paging operator and take the message for you and then send it and it'll go out through the digies. Um, cool. So, last slide. Um, if anybody would like a bleepy, that is my van. I'm behind stage C. I'm I'm going I've got 40 of these I've managed to make. So, these are artisan hands soldered. I've got the burns to prove it. Um, devices. So, I'm going to do 20 today and 20 at the market tomorrow, the expansion market in null sector. Um, they're 20 pound each, which is basically what the components pretty much cost me. rounds up. I think 18 something for the bill of materials. Um I'm going to kind of say one per person. I Please don't kind of turn them and say I want four of them and and take all of them. Um uh it is plugand prey operation. So it should all just plug into the badge. It the app is on the board. It'll auto launch the app. If you've got the latest the 2.0 firmware, it'll then add it to the menu of the app. Um if not, I'll explain it to you later. Um I've also got some bare PCBs. So, I've got 40 madeup devices and I've got 50 just the PCB boards and you need to buy the components. Um, which is again about about 1516. Um, it's a an RP 2040 Raspberry Pi Pico uh tiny version. Get it from the Pi Hut for a fiber a PO speaker and then the little radio module which again I'll give you the link on Digi Key. Um, and you can just solder the three components onto the board. It's not It is hand solderable with a soldering iron if you're a little bit of patience. Um, and you can build your own one. They can also be used over USB without the badge. So, you can plug the USB into it and use it via serial as a as a paging gateway. And with a minute and 90 seconds to spare, that's it. That's my contact details. Um, my website is samin.com. Sam everywhere. My deck is 95. Um, thank you. [applause]