Radioshack Phone Dialer – Red Box

i thought i’d start out with this hack while we’re in beta, since it was one of the first ones that really got me interested in the way phones worked and how many consumer electronics can be used for new and educational things. a “red box” was a device that would simulate coins being dropped in to a pay-phone, hence free phone calls for many people until the phone systems changed. the most popular device to modify was a radioshack tone dialer, a simple solder of a 6.5536 mhz crystal was all it took and you could “drop” 5, 10 and 25 cents at a time to make calls.

We really didn’t want to edit this because it’s a repost of the first Hackaday post ever, but [Phil Torrone] and [ladyada] dug out the old RadioShack pocket tone dialer, found a payphone (!), and tried it out:


RadioShack does not sell the pocket phone dialer anymore, but they do sell a DTMF chip (an NTE1690) that can do column D (the interesting bits that make all the phreakers happy).

We’ll probably end up reposting this one in another ten years.

58 thoughts on “Radioshack Phone Dialer – Red Box

  1. These were briefly popular my Freshman year of college. After a few months, the payphones (remember those?) were all removed from the dorms with an official but slightly tongue-in-cheek memo from the phone company claiming that the phone were no longer “profitable”. Seriously, those things were used 24/7 for long distance (when that meant something) and international calls with their coin boxes all but empty!

      1. Might I suggest a better system to browse the archives? Unless I’ve missed something, you have to go back month-by-month to see previous posts. Is there another way to do this?

        It’s awfully painful to go back 10 years this way.. ;)

        1. Click on ‘older posts’ and notice the URL you get. It should look like this:

          If you were to change the 2 to something like 1000, you’d find yourself looking at posts from 2012, Currently page 2427 is the start of time featuring this post. Of course HaD could provide a nice flexible user interface to do this, so we wouldn’t have to resort to a hack…

    1. sweet, and the human (hacker) would be confused to boot! (they sound simillar?)

      PS: to get 300 baud on certain stock Arduinos is impossible,
      so change the clock crystal to NTSC color (3.5879xxxxx MHZ ?) and edit boards.txt

  2. 10 years ago i started this site to celebrate makers, hackers, artists, engineers and anyone who wanted to share their projects. thank you everyone who’s been part of this site all these years – reading, contributing, sharing and being excellent to one another. 10 years goes by pretty fast :)

    1. I’ve been here for 9.5 of those 10 years and I’m deeply indebted to you, Phillip, for what you’ve created… my thanks to all the editors/contributors over the years (of course) but a tip of the proverbial geek hat to you specifically. Cheers!

  3. I remember the Good Old Days with digital versions of the “Anarchist’s Cookbook” and “Poor Man’s James Bond” circulating around the BBS(NPD, of course) and Usenet circuits.

    Ah, memories.

  4. I believe the statute of limitations allows me to publicly admit that I made one of these when I was in college too. I didn’t use it a lot, though, because I lived in an off-campus apartment, so trekking off to find a payphone to make a long distance call was more trouble than it was worth, and really the only people I wanted to call long distance were my parents anyway.

  5. Happy 10th anniversary HAD! Boxing was a great way for an elementary school student to learn about electronics and keep in touch with his sometimes girlfriend who lived far enough away to be a long distance call. It was also a great way to learn to recognize surveillance vehicles outside the local Radio Shack and those that hovered near payphones outside the Aladdin’s Castle arcade. Thanks also to Capt’N Crunch and Woz for what they taught in “Prodigal Son of Silicon Valley”. A young boy was mocked at the local bookstore for special ordering such a “weird” book. If they only knew. [somewhat evil laugh].

  6. This kind of reminds me of a non-technical “hack” that I used in college. I was just a little bit late to get to enjoy red boxes but I did make a lot of long distance calls.

    The local gas station sold calling cards. For you younger people a calling card gave you prepaid phone minutes. You call a 1-800 number (free) type in a code number off of the card and then you typed the number you wanted to reach. The computer at the other end relays your call to it’s destination and disconnects it when you run out of minutes.

    Anyway, the gas station sold two cards, both the same price. One card gave you several hundred minutes but there was a catch, every call you make automatically dropped a bunch of minutes. If you wanted to make one long call last all day long it was a good deal. Otherwise… not so much. The other card didn’t do that. You could make as many calls as you wanted but it didn’t come with very many minutes initially.

    The two cards had different images printed on them, different company names and different call in numbers. Still, somehow I had a hunch that both cards were from the same place. Maybe because gas stations always carried both? Maybe the identical price or something in the printing process used? I don’t remember.

    The “hack” I found was to buy the card with the big minutes. Then, call the 1-800 number from the card with fewer minutes. The same pin number worked! I was using minutes from the same account. But.. the low-minute number didn’t do the per-call minute subtracting that the other number did.

    This trick made those otherwise sketchy, ripoff calling cards into the cheapest long distance service I could ever find until cell phones made long distance charges obsolete.

  7. You would think Hackaday would have a super duper contest the celebrate the 10 year anniversary! :) Here’s to many more years of success. Keep on truckin ladies and gentleman on the Hackaday team.

  8. Well back in the day the late Walter T. Shaw from AT&T made the first “blue box” to make free toll-calls. Then he invented the “cheese-box” (call diverter) for the mob (i.e. bookies, etc.) and still used today by spooks. However, red, blue, and others no longer work for obvious reasons. Walter did FEDERAL time too.

    But if you want to do it for free and be totally legit. Try this idea (you’ll have to think outside the box on this one):

    1. Get a Skype acct.on your home PC.

    2. Get a ASP Hosting service like to write ASP (active server pages) in VBScript.

    3. Write a Javascript app that monitors a webmail box for keywords in the subject line or body for two callback telephone numbers. May need ASP screen-scraping code to get keywords and numbers for your JS code.

    4. Then this triggers a subroutine that deletes the email (so it wont reiterate), has Skype conference dial the 1st number (party you are calling), and the 2nd number (link back number to you) of the payphone you are at.

    5. Payphone will have to say on front label that it “accepts incoming calls” or none of this will work.

    6. Then send your PC at home a SMS text message with a trigger keyword and 2 phone numbers. Then the payphone rings with your party connected already.

    7. Skype system will drop on its own when everyone hangs up.

    Step #6 will work with just about any dumb cell phone with SMS which is common. However, if you have a SmartPhone with web access you can set up a HTML web page with JavaScript and just do a form send to the webpage with the query strings set for the 2 telephone numbers. Then (in both scenarios) use the Skype URI’s (skype: or callto:) to setup a conference call (i.e. skype:+1-202-555-1212;+1-703-351-1100;) notice you must use semi-colons (;) as separators and use +1 for USA or it wont work. Hyphens are not needed.

    *** But if you already have a CELL PHONE in your pocket why would you need this system to make free calls from a payphone? ***

    Another twist that eliminates the cell phone all together involves a old-fashioned modem with caller-id function:

    1. Get this modem. Its called a voice data modem I think. The AT Command set must respond to AT CID=1 (I think).

    2. Get a private line from your TELCO no one will ever call except you to avoid false triggers. Or just use your regular TELCO number and set the trigger to 3 rings or something like that, no rollover to voice mail or answering machine. Hopefully a human wont answer either.

    3. Write in your favorite code (like VB – Visual Basic) that can monitor a serial port input to your PC for caller-id text. The code will need to extract the caller-id text to use as a callback number. Set a conditional IF THEN subroutine to look for 3 rings from modem first (will also be text from modem i.e. “RING” – set up a FOR NEXT loop for that. Count off 3 rings.).

    4. Call your private TELCO line from a payphone (put 1 or 2 quarters in first – you’ll get them back). Let it ring EXACTLY 3 times then hangup (TELCO phone never answers). When PC is triggered have VB open a web link using the Skype URIs mentioned above. It will only VOIP call that caller-id number back at the payphone you are at. Your TELCO line is not used any more. You only needed it to capture caller-id and trigger only.

    5. When you answer the now ringing payphone, the PC has you audio-linked to a WINDOWS built-in voice recognition program via a speaker phone or some sort of audio connection from SkypeOut program (no headphones – just loud speaker and mic attached) to the separately running voice recog program (in VB or Javascript – VR is in global dictation mode). The VR program listens continually for the correct words like:”COMPUTER: 202-555-1212 dial.” – it responds in text-to-voice toward the Skype microphone “Computer dialing 202-555-1212. Please hangup now!”. It only needs you to hangup the payphone so you can receive following payphone incoming call – nothing to do with your TELCO line at all.

    (Please note VR tends to return numbers spelled out in words. You will have to write a subroutine to convert these words to numerical and remove all spaces for Skype to use them.)

    6. You’ve hung up the payphone now. The PC will now open a web link to the SKYPE URI to do a Skype conference call mentioned above. It will not be using your private TELCO line anymore. It will now be a SKYPE VOIP call. The 2 numbers it dials is your target number and your caller-id number from your payphone. If payphone does not send caller-id then your screwed. Go to another one that does.

    7. Skype drops all calls when both parties hang up. So you don’t need to be concerned about dropping Skype after the call.

    This VR thing may sound like such a hassle at first. But there is no other way to dial the target desired number. It can only be discovered by you saying it to a VR program or live operator. You could make a DTMF decoder but that’s too much technology when you already have free VR built-in.

    Also if anyone could think of a service for BLIND people (you’d be faking being a blind person) that dials numbers automatically free via a live operator or automated attendant, then that could be the 2nd number ALWAYS dialed by this system eliminating a lot of steps above. So far GOOG-411, TELLME, and BING411 wont work for you. Also Skype can not dial 0 for operator nor 711 for handicap.

  9. I just realized that I left a whole bunch out in this comment:

    “However, if you have a SmartPhone with web access you can set up a HTML web page with JavaScript and just do a form send to the webpage with the query strings set for the 2 telephone numbers.”

    This will not work without your home PC being involved. As stated above this will only work locally on your SmartPhone’s browser which would be totally pointless. You will have to use ASP to write a FSO object in text (Field Streaming Object). The information is posted to a FSO write object on your ASP providers database fileserver and your home PC scans every 10 seconds for text updates to the FSO Read object.

    When it sees the proper text it triggers and deletes old text so as not to reiterate. Then your PC Skype dials accordingly. It wouldn’t be a good idea to open this up to the public as the Skype phone calls would be out of control and your own phone calls would be impacted. Keep it private and you’ll be the only one using it and you won’t get dropped mid-call while some other joker makes a call of his own.

    1. and even if the phone does not mute the mouth piece before paying modern payphones may have an extra switch contact on the totalizer that will modulate the line voltage much in the same way that rotary dial does so when the phone co switch hears the tones they also get a pulsed signal at the same time indicating a payment.

      1. This was the basis behind the WarGames soda tab hack: the center contact of the carbon mic was directly connected to the ring line, while the phone chassis ground (and metal anti-vandal cord) was connected to tip. Unscrewing the mic and connecting the spring contact in the handset to the phone chassis with a chunk of metal would simulate correct change being inserted for a local call.

        Eventually payphone owners got wise and started gluing the caps on. But since the mic was nothing more than a can of carbon granules, you could get the same effect with a sharpened nail driven through the center. Of course I wouldn’t condone this as it’s both vandalism and theft and has good odds of killing the mic entirely (not that I’d know…)

        Not sure if this is still the case, but I also can’t remember the last time I needed a payphone.

        1. “Punching pay phones.”

          Push a nail through the speaker foil in far enough to temporarily short out the (Bell) pay phone line itself.

          It only worked for local numbers, though. Dial the first 8 digits then on the 9th digit, press the number and “short” the nail against the side of the pay phone. This grounded the high voltage “coin check” signal sent by the switch and let the phone dial out.

  10. reminds me of that picture floating around the internet where
    a guy is standing at a payphone and holding the handset onto a small portable computer with built-in acousticaly-coupled modem.
    all while wearing an (80’s) buisness suit and carrying an (80’s) briefcase.

    i assume he was a successful stock-trader
    cuz he was carrying around 1000$ (4000$ today) equipment
    just to be able to exchange info with a computer while in public without waiting to get into a hotel with power and tel. line.
    … back then he couldnt “just stop into an internet cafe for 2$” … there was no internet!

  11. I’m not sure if they stopped this during the 80’s, but I clearly remember still being able to do this during mid to late 90’s. The phone dialer was a neat device that I actually used it for it’s intended purpose back then. The only slight difference I did was to add a microswitch so I can switch between the crystals. Eventually I just ended up getting a small keychain recorder to record the tones.

  12. I found Hackaday in 2005 as well. It quickly became (and still is) one of the first sites I check in the morning.
    Phil, Eliot, Ian, Caleb, Mike, Brian, and everyone else who made Hackaday what it is today – Thanks for 10 years of covering (and creating) awesome hacks.

  13. I tried this back in high school, early 2000’s. except I dialed the operator and played a couple of tones. The operator said “I know what the hell your trying to do here, I’ll give you an A+ for effort though, gimme the number you are trying to dial and ill connect you”

  14. If anyone still uses a payphone these days, which I doubt, all the old phreaking methods are pretty much countered by modern TELCO technology. HOWEVER, there is still one method not countered yet. It uses social engineering. Don’t do this too much as it will get countered and it will dry up.

    Go to any payphone and if you get a dial tone press 00. If not you will have to put in the required coins (you may or may not get them back). The operator who covers the payphone provider will answer. Say : “Operator I’m getting no ring every time I dial 202-###-####…”. 90% of the time she’ll say I’m sorry and she’ll dial it for you free. However that unlucky 10% she’ll say “Please deposit $##.## in the coin slot…”


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