Computers & Mobile Technology
DIY Hacks & How To’s: Get Emergency Power from a Phone Line

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What do you do if the power is out, but you need to charge your cell phone to make an emergency phone call? In this episode of DIY Hacks & How To’s, I show you how to tap the power flowing from your phone line.

There is a small amount of electricity that is constantly available in a phone line. This is what powers traditional corded phones. Because the phone system is independent of the power grid, the phone line generally even has power during a black out. While this is not a lot of power, it is enough to charge your small electronics such as your cell phone or other USB device. All you need is a simple voltage regulator circuit.

Complete step by step instructions can be found at:

See the full series here.

49 thoughts on “DIY Hacks & How To’s: Get Emergency Power from a Phone Line

  1. but wait, if you’re powering your phone from a phone line to make an emergency phone call, why wouldn’t you just use the phone line to make the call? now, if you need to charge because you want to play angry birds, well ok then ! ;)

      1. In the US, (and the UK I believe) telephone companies are required to keep lines active for emergency services routing even if they aren’t activated.

        In other words, as long as your line is connected and has a tone, you can call 911.

        1. You’re mistaken. The US phone companies are not required to keep the lines powered with no subscriber service. No service = no line power and of course no dial tone.

          1. if the person doesnt have a phone like but does have it connected to the pole they will get a ringtone, if it is not connected to the pole, then they would have to open the box and they would be able to plug in a phone there to get a ringtone

        2. The requirement to allow emergency calls without active subscriber service applies only to cell phones. It does not apply to landlines.

    1. This is indeed the case in the UK, I’ve found active lines with dialtone that would accept emergency calls and engineering circuit test numbers even in property that was unoccupied for several years.

  2. This is interesting though I wonder why you wouldn’t just plug a phone into the phone jack to make the call ;)

    1. @chuck, this is where you get to laugh and mutter ‘Kids those days…’. This hack is old as sin, even though people used to power different stuff in the past (cd player, radio)… But it is good to see a new version of it.

        1. Dunno how old “Sin” is, but I was stealing power from phone lines in 1958. That’s 55 years ago.

  3. While this may work in some minor cases, this is a bad idea.

    Generally your phone is expecting to be charged from a usb (or similar power adapter), which outputs 5V at 500mA. The 75mA at 5V the writer is getting from the phone line is generally not enough to charge a phone. This hack will definitely not work with an iPhone as they require special voltages on the two data lines in the USB port.

    This hack also has the possibility of damaging the connection to the phone company. Then not only do you not have power, but you have no way of making an emergency phone call (the reason phone lines stay up when the power is out).

    In addition, if a phone call is received while using this device, the regulator could be damaged due to the high voltage on the line during a “ring” signal. The 7805 datasheet states that the input voltage should be below 25V. This voltage could be exceeded during a ring, even with the series resistance of the line. A damaged regulator could expose your phone to the line voltage, surely destroying at least the battery charger, if not the whole phone.

    1. This guy speaks truth. The voltage not only *could* exceed 25V, it certainly does. Minimum ringing is 40V, the systems around here are 120V. Dumping 120V AC onto your little circuit and device is what we call a “bad plan”. I have empirical experience; I was a phone tech about 10 years ago and we routinely make physical contact with the circuits. I was bitten more than once by a ringing line while searching for my circuit.

      1. I concur with the ring voltage. It’s been a couple of decades but the Australian telephone system uses 50v ring and when it goes up your arm you know you’re alive and adrenalin is pumping. More importantly anyone contemplating this project should also check to see if there are breaking any laws. Australia, and probably New Zealand too have very severe penalties for attaching any device not approved by the telephone authority, and this device would not be approved. There other alternatives you can use. I use an external battery pack with multiple voltage ranges of 3 to 12 volts and it has a belt clip so you can be an ultra nerd.

    2. To be honest, the Telco lines will happliy drive a short circuit at low current (limited to the 75-80 mA he’s getting here), so I don’t see how the line card could be damaged.
      Ringer voltage is more problematic, but protection could be added to the design.
      Best design might be to have the circuit maintain charge on a small battery, which could then provide bulk power to the USB 5V regulator.

      1. It’s more the voltage than the current which would be problematic to a 7805 in the case of a ring. Around here, lines ring at about 90 volts AC and if you can picture a house containing several old fashioned mechanical ringers all being simultaneously driven by the phone company’s juice, you should know that there is also plenty of current at certain times, as in during a ring. Very low impedance applied across the wires (as in the extreme case of a direct short) signals the phone company’s equipment that the phone is off-hook. If it was ringing, the ringing voltage is ended, and then a far lower voltage & current is supplied to power the voice circuit.

        The availability of any voltage at all on the line implies that there is active subscriber service, thereby rendering the need to make an emergency call on a discharged cell phone somewhat moot.

        The presence of active subscriber service on the phone line implies that depending on numerous conditions (especially whether someone is calling the number, and what the device’s impedance is, whether another phone on the same line is off-hook) the line voltage may vary – and dramatically. If the voltage exceeds the maximum ratings of the 7805 device, which would be the case when the line rings, you could be dumping 100+ AC volts right into your iPhone. Think about it.

        Finally, not that many people here would care, but it is actually illegal to connect a non-FCC approved device to the phone line. That could only be done with permission from the phone company, and they are NOT going to grant permission for such a thing.

        PS: The cell phone in the picture does not appear to be charging.

        PPS: This is possibly a way to disable two phone numbers at once. Where’s your emergency call now??

    3. I assume you could wire this up with some kind of voltage limiting and a capacitor setup such that the capacitors would charge the phone once they were charged and the current would be enough to keep the capacitors charged up. There would be an initial delay with the initial capacitor charge of course, but that’s trivial.

    4. Agreed; I do not find any 5V regulators that can handle over 50V in.
      Agreed2; 75mA would take a very long time to charge, if at all.

  4. I wonder how stable the voltage level is on the regulator output without any capacitors on either the input or the output. Some linear voltage regulators will be unstable and oscillate without them.

  5. Apart from many good reasons above why this is kind of useless, and perhaps a bad idea, I believe it’s also in a legal grey area. The FCC provides guidelines for what constitutes Part 68 Compliant Terminal Equipment. TE that’s not specifically Part 68 approved may be illegal.

    BTW: you could probably fend off any incoming ringing signals by seizing the line with a 600 ohm load across it. 600 ohms will cause the line to appear busy to the telco, and thus protect you from getting a 48v ringing signal.

  6. Here in Australia you cannot attach any devices to the phone lines unless it passes standards testing. Do yourself a favour, buy a $50 backup battery to keep charged for emergencies. Or go get a small solar panel device. I also believe the telcos can and do monitor power draw on phone lines and could probably isolate your problem connection fairly quickly. Our phone lines also have maximum REN loadings

  7. …the illegality is also defined in the Criminal Codes. It’s plain theft. As is any “unjust enrichment”, such as the acquisition of electric power without proper permissions from the owner of said network.

    I’m unaware of the legislation regarding complicity in the US, but in many European countries this guide could be considered as aiding theft.

    1. Fortunately in the US we enjoy broad first amendment protections that acknowledge the meaningful distinction between talking or writing about doing something and actually doing it.

      1. I know. Bradley Manning is thankful for that. And it’s not like the legislator is trying to undercut it. SOPA, DOPA, COPA, PIPA, DCMA. Chaplinsky v. New Hampshire (1942).

        I’m not promoting any country, federation, bundesrepublik or union. Just wanted to inform the previous commenters of a more specific illegality.

        1. As a point of interest – In the US “Unjust Enrichment” is a civil law concept, not a criminal law one. A national “Simple Theft” doesn’t exist n the US, either. Aside from certain very particular varieties of stealing, it is left to the states takes care of that kind of thing and their laws vary. Most theft/larceny laws are restricted to property, but most states have a “Theft of Services” charge which could conceivably be applied to something like this. As to the Bradley Manning non sequitur, understand that Manning isn’t being tried in the criminal justice system, he’s subject to court martial by the military – Civilian criminal law doesn’t really enter the picture, it’s all about the UCMJ. “(The Supreme Court of the United States) has long recognized that the military is, by necessity, a specialized society separate from civilian society…(t)he rights of men in the armed forces must perforce be conditioned to meet certain overriding demands of discipline and duty.”[Parker v. Levy, 1974]

  8. I beg your pardon, but you are mistaken. Your comment should’ve read:

    “It’s always nice when a truly excellent internet blog tells you how to commit a felony.”

  9. So much hatred. The article clearly states that this is for emergency purposes. If you have no other options and absolutely need to make a phone call during an emergency, I doubt you’d care if it is illegal, or bad for your phone, or may not work, or whatever else the comments say.

    1. Not hatred, just open, healthy exchange of information in pursuit of learning truth. Hatred is the desire to kill someone for your own selfish reasons. Big difference.

  10. In Horowitz and Hill’s The Art of Electronics 2nd Ed there’s a section on using the power the phone company supplies to run low-power circuits. In the ‘off-hook’ state you can draw a minimum of 26 mA at a voltage of between 6 and 8V. Impedance at audio frequencies is 600 ohms. That’s more than enough to drive some quite interesting circuitry. For those interested, it’s section 14.05, starting on p. 935. Pay heed to the warnings about what you are allowed to do both electrically and legally.

  11. Hi Everyone

    I have made an emergency LED lamp here in New Zealand just for an experiment . It works fine but after turning the lamp on I rang the landline on my mobile and the line was “busy” so the phone didn’t ring but according to the website where I got the circuit diagrams from the phone could still be used as normal ( being a us site I guess phones may work abit different here in New Zealand . Yes it may be illegal to tap into the electricity from the phone line but I agree during an emergency I don’t think anyone will be too worried about “the rules”. If I have to plug in my emergency lamp to have light to find the corded phone I will go right ahead and do it :-)

  12. PS

    Hi Guys

    I also forgotten to mention I read above about mention of non approved devices being illegal to use on phone lines etc.

    I found this website sometime ago and I rang up and they were sold out and I would be waiting for quite sometime for more to come.

    Look up Telco Powered Products (

    You mite find the link interesting

  13. I’d just place the emergency call with the landline phone instead of taking the power from the line to charge the cell phone ;-)

  14. That means 7805 is for 5 volt output.

    Let me know the Voltage regulator number for 12 Volt output?

  15. This works. But there are caveats. If the phone rings (which is the most likely way of communicating during and emergency when power and cellular may be down), your circuit will get fried as voltage spikes to unto 90v during the ringing process. You need resister or diode or something to reduce the power when it spikes.

    You can continue to receive calls when this is connected if you have a splitter or other phone outlets. While on the call, the voltage drop makes it nearly impossible to continue to charge. After you hang up, charging can resume.

    As a whole, this is clever enough that I am surprised there is no out of the box solution sold on eBay or Alibaba.

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My name is Jason Poel Smith. I have an undergraduate degree in Engineering that is 50% Mechanical Engineering and 50% Electrical Engineering. I have worked in a variety of industries from hydraulic aerial lifts to aircraft tooling. I currently spend most of my time chasing around my new baby. In my spare time I make the how-to series "DIY Hacks and How Tos."

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