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PART 1.1: 📞 How Phones Worked - Why Picking Up the Phone Was Magical

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By Kay
6 min read
PART 1.1: 📞 How Phones Worked - Why Picking Up the Phone Was Magical

A Real Story

Somehow, I was feeling nostalgic. Remember back then… when I was only 12 years old? My home didn’t have fancy mobile phones, or private wireless base stations.

We had just one home phone line that connected to several handsets-one downstairs, one upstairs.

In that cozy two-story house, I used to sneak onto the second-floor phone like a curious little kitten.

Whenever my father picked up the old-school phone downstairs, and I picked up the one upstairs, I could hear him talking. (Whether I could hear both sides of the conversation or just my father, I honestly can’t remember now-most of the details are fuzzy. I just remember the magic of listening quietly without them knowing, as long as I picked up the phone at the same time they did.)

It felt like pure magic. And even now, I still don’t fully know how it worked.

So today… I’m going to pull back the curtain and reveal the secrets under the hood - with some delicious phreaking history and old-school hacker stories along the way. 🚀📞✨

🔌 How Old Phones (Landlines) Actually Worked Inside Your House

Imagine back when you were a little girl/boy, sitting upstairs in your house. 🏡 You picked up the old-style phone while your father was already on a call downstairs.

But WHY could you “join” the call quietly?
Because all the phones inside your house were wired together into one simple electric loop. 🎈

Here’s the magic behind it:

🛜 Step-by-Step Inside the Old Phone System (Plain Old Telephone Service - POTS):

  1. Shared Loop:
    Your house had one copper wire pair coming in from the outside telephone network.
    • It carried both the ability to ring the phones and carry voice conversations.
    • Every phone inside the house tapped into that same wire. 📞➰📞
  2. Idle State:
    • When nobody picked up, the phone line stayed at about 48 volts of DC electricity. 🔋
    • The phones just “listened” - no active voice signals yet.
  3. Pick Up = Close the Circuit:
    • When you (or your father) picked up the phone handset,
    • it closed an electric circuit inside the phone.
    • This “loop closure” told the telephone exchange outside:
      👉 “Hello! Someone wants to make or receive a call!”
  4. Ongoing Call = Active Circuit:
    • Once connected, your voices were converted into tiny electrical signals 🧠⚡
    • These signals rode the same wire to the telephone company’s switching center, and to the person on the other end of the call.
  5. Sneaky Pick-Up:
    • Because all phones at your house shared the same loop,
    • If you picked up another phone during a call,
    • your handset got connected to the same ongoing electrical conversation!
  6. No Notification:
    • The system was too simple to detect “Hey, a second phone picked up!”
    • There were no smart processors yet - so you could listen without anyone knowing. 👻

🌟 Tiny Visual Story (Imagine This)

1
2
3

[Outside World] ---(wire)---> [House Main Line] --+--> [Father's Phone] (picked up)
                                                 |
                                                 +--> [Your Phone] (picked up silently)

Both phones share the exact same conversation path, like two straws stuck into one soda! 🥤➰🥤

📞✨ Q: Why Idle Voltage is 48V in POTS

First, even when no one is calling, even when the phone just sits there,
there’s 48 volts DC sitting on the line.

But why 48V, specifically?

Here’s the inside story:

📚 Reasons for 48V:

  1. Signal Readiness:
    The telephone exchange (the big switching machine downtown) needs a way to know whether a phone is “alive” (on hook) or “wants to talk” (off hook).
    • 48V gives enough electrical “presence” for detection.
  2. Powering the Phone Itself:
    Old landline phones didn’t plug into wall power. ⚡
    • They pulled power from the phone line itself!
    • (That’s why during blackouts, your wired phone still worked - magical, huh? 🧙‍♂️)

  3. Protection from Noise:
    Higher voltage helps overcome little bits of electrical noise or leaks in the line (countryside wires could be messy!).

  4. Safety First:
    48V is high enough to be functional but low enough to not kill you if you touch it accidentally.
    • (Though it can give a nasty zap!)
    • It’s below dangerous shock levels under most conditions.

Fun Fact:
Actually, it’s often -48V (negative voltage), not positive - because using negative prevents corrosion on the copper wires. ⚡➖

⚡🛜 So, YES:

Even when idle,
your POTS line is sitting there quietly sipping electricity.
Not much, but always alive… like a cat half-sleeping but still listening. 🐈‍⬛✨

🧮✨ How much electricity does it consume?

Now let’s get nerdy and cute, okay?

Let’s calculate an estimate:

Step 1 - Normal Idle Current

When the phone is idle (on-hook), almost no current flows.
The circuit is open, meaning the electricity is “waiting” but not really “moving.”

  • The line is sitting there with 48V applied,
  • But the current flow is tiny - basically in microamps (µA) range.

Typical idle current:
🔹 Around 2 to 20 microamps (depending on line condition).

Step 2 - Power = Voltage × Current

Let’s take the middle estimate:

  • 48V × 10µA (microamps) = 0.00048 Watts

(Yes, less than half a thousandth of a watt! 😱💡)

Step 3 - Energy in a Day

Energy (watt-hours) = Power (watts) × Time (hours)

  • 0.00048W × 24h = 0.01152 watt-hours per day

That’s basically nothing.

🧡 In Short:

ItemEstimate
Idle voltage-48V
Idle current~10 microamps
Daily energy usage~0.012 Wh
Daily electricity costWay less than 1 cent!

You could leave that line connected for 10 years and barely notice anything on your electricity bill. 😹💡

🛡️💬 So Conclusion:

  • Yes, POTS always “consumes” tiny electricity when idle.
  • But it’s incredibly tiny - like a single breath of wind pushing a leaf 🍃.
  • In that countryside house? Probably so little the electric meter doesn’t even blink.

🌟 End Summary for Part 1.1

TermMeaning
POTSPlain Old Telephone Service - the basic old wired phone system.
Copper Wire PairThe two metal wires bringing telephone to your house.
Idle Voltage48V of electricity when phones are “waiting.”
Loop ClosurePicking up the phone completes the circuit and signals the network.
Shared LineAll home phones shared the same wire loop.
Sneaky Pick-UpPicking up another phone connects to the same call without alert.

🎁 Tiny Treasure Box (Optional Curiosity Dive!)

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☎️ phreaking
📝 Series ☎️ Phreaking 🛜 Plain Old Telephone Service (POTS) 🧩 Shared Line Magic 🧠 Electrical Loop Closure
This post is licensed under CC BY 4.0 by the author.