How To: Hack Your Old Phone Line into an Emergency Power Supply for Your Cell Phone

Hack Your Old Phone Line into an Emergency Power Supply for Your Cell Phone


If telephone titan Alexander Graham Bell had his way, we'd all be answering phones like Mr. Burns. Thankfully, frienemy Thomas Edison had enough sense to realize we weren't always on the briny. He preferred "hello" as our standard telephone greeting, which he is credited with coining in 1877.

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Fellow American pioneer Davy Crockett actually used it as a greeting first in 1833 (as compared to an exclamation)—but in print, not over the phone.

"Hello" is also the recommended greeting published in the first ever telephone book from 1878 (actually, it was "hulloa," but close enough).

Since then, the landline telephone had been our primary method of long distance communication—until now. With the widespread adoption of cell phones in the states, "hello" is the only thing sticking around for the long haul.

I can definitely say that this thing is not:

No, it's not an Ethernet port that somehow shrank. This not-so-newfangled contraption is called a telephone jack, and if you're like me, you haven't used one in at least a decade or so.

You may not even notice them anymore, but if you look around your house or apartment, you've probably got at least one or two of them on your wall. Or, something that looks like this:

Now, here comes the interesting part of the story—they are not useless.

Using Old Phone Jacks for Smartphones

While a cell phone is incredibly convenient, without a charged battery it's just useless weight. If a storm causes a power outage in the area, I'm not looking for candles and flashlights—I'm figuring out how to charge my iPhone!

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There are a few well-known options for charging your smartphone without help from the electric company, including charging cases, car chargers, power inverters, laptops, and more.

However, something we all have readily available already is that old landline jack. Corded phones don't need to be plugged into a power outlet; they actually get enough power to operate from the phone line itself. When the power goes out, land lines will still operate on their secondary source of power feeding from the telco. Meanwhile our cell phones will slowly drain and die.

With this simple hack, you can put that old relic to good use and convert it into an emergency power supply for your smartphone.

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You'll need a regular USB cable, your cell phone's USB charging cable, an available phone line, a phone cord, a voltage regulator, and a multimeter.

The multimeter is used to check the voltage of the jack in question and the voltage regulator keeps the output at 5V. The regulator makes a simple circuit with the phone cord and USB cable to convert the phone signal into power that your phone can use.

Check out this video guide by Make to see how it's done.

And take a look at the complete guide by Make's Jason Poel Smith over on Instructables to see the process step by step.

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Photos by Loren Kerns, Foxpa, Cult of Mac, Hana/Shutterstock, James Steidl/Shutterstock


in india landphones are widely used, but it is true that the trend is slowly diying.

Yeah very true. When I went to Nigeria a few years ago, every house used a landline phone, while few even had cell phones. But within the next decade or so, I am sure the trend in the States will spread to places abroad.

why phone can charge ? i remember just usb is 5.1 Vol can charge for phone, somebody advise ?

Watch out for the ring voltage! I'm not sure your average 7805 regulator can handle it!

That means 7805 is for 5 volt output.
Let me know the Voltage regulator number for 12 Volt output?

can you not just attach the red and green wire directly to the plug that came with your phone, and then attach the usb? seems a lot simpler and you'd always have the correct amount of electricity, even with a surge.

No, The operating voltage is 50V on a base telephone circuit. Without the regulator in the circuit it will look like a short causing the circuit breaker at the telephone exchange will trip and cut power to the line.

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