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While it's possible that cellular calls can be listened in on, it's one of those things where somebody would really have to go out of their way for it to happen.

I crossed paths with someone who I believe is a bad person in a professional setting and I'm afraid that they know that I know something. Do you know if it's possible for somebody to listen to my cell phone conversations remotely? I've never used the phone for internet and nobody has physical [access] to the device but me and I do not use Bluetooth. It's a Boost mobile phone. I don't expect that you'll have time to answer this especially because it's not directly a computer a question, but if you do, please don't include any identifying information.

In this excerpt from Answercast #60, I look at the problems and possibilities of eavesdropping in on cellular phone calls.

Cell phone snoops

Well, OK, no identifying information included other than the fact that you have a Boost phone.

So the short answer is yes and no.

Here's the problem. First of all, old analog phones (which I believe are actually no longer supported by the network) - absolutely! They could be listened to. They are simply radios and radios can be listened to with the proper equipment.

These days, all of our mobile phones are digital. Even when we're not using mobile data, the actual phone calls we make are converted to digital data.

Calls are encrypted

That digital data, as it turns out, is indeed encrypted. The intent is that the data cannot be eavesdropped on as it's transmitted over the air because it is still fundamentally a radio and anybody with a radio tuned to the right frequency could technically listen into the data.

That's why encryption is important.

Now, here's the bad news: the encryption standard for most of our digital phones these days is so old that it is designed to work with very, very weak hardware: what today we would consider to be very, very underpowered hardware.

What that means is that even though it's encrypted, it's actually not that hard to decrypt. The algorithms aren't that strong and the amount of processing power that it takes to decrypt a telephone call these days isn't really that much.

Equipment and range

Now, to go back to some good news here, it does take special equipment. So someone would actually have to have a specific intent to go out and start eavesdropping on cellular phones in order to be able to eavesdrop on your phone. And yes, they would need to be within range; within radio range of your phone.

So, consider what the range of a phone is. In line of sight, it's what? A mile, two miles? Whatever the distance is to your cellular towers that it's connecting to.

So the chances of somebody actually going through the effort (even though it's not computationally expensive)... the chances of someone getting the specialized equipment to be able to do this, setting up the software to be able to decrypt what it captures - that's not really that common. It's not something that I worry about very much at all.

If you are of course the target of somebody who has the ability, who has the resources, who has the desire, who has the whatever, to do this, then yes, it's certainly possible.

Cell phone privacy

I certainly wouldn't consider a digital phone call to be private for example from (I don't know...) intelligence agencies worldwide. The encryption just isn't that strong. You'd probably want to layer some other kind of encryption on top of it.

But the short answer is that while it's possible that cellular telephone calls can in fact be listened in on, it is difficult enough that it is just one of those things where somebody would really have to go out of their way for it to happen.

That's unlike wireless networking or Wi-Fi - where anybody with a laptop basically has everything they need to listen in to an open Wi-Fi conversation. All they need is some software and the software is available for free.

When you go to things like cellular phones, digital cellular phones, you need specialized hardware, you need specialized software that most people don't have - and to be honest, I wouldn't even know where to start to go get it.

Article C5908 - October 11, 2012 « »

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Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

October 12, 2012 10:36 AM

I'm not any expert on cell phones, but for your info it is not hard to hear persons calls. I recently bought a set of stereo head phones, Sony, to listen to my living room tv as my wife complains its too loud. The Sony headset is TMR-RF970R and it says it is a RF Stero Transmitter. (e.g. the
headphones connect wirelessly to transmitter connected to the tv.) One morning, crystal clear, my headset picked up the neighbor, talking on her cell phone or maybe her portable phone. The Sony headset has a switch for 1,2, or 3 channels on the 2.4 gighertz channel... I never investigated further as I set up tv channel, but at the time, I had no trouble hearing her conversation. I am 30 ft from her condo and just a concrete wall dividing us. I am writing this becsause you were quite explicit in saying its not "easy" to capture phone conversation; with this wireless headset, it was very easy to pick up the conversation.

That's not a cellular/mobile phone you heard. Cell phones all transmit digital data these days which would not be intelligible on headsets as you describe. More likely a simple cordless home phone, which does operate in the 2.4ghz range.

Ken B
October 12, 2012 12:06 PM

John, there is a world of difference between a cell phone and a cordless phone. Leo was talking about current cell phones. Cordless phones vary from manufacturer to manufacturer, and may be no more than an analog radio, just like the old cell phones Leo mentioned. While many cordless phones nowadays are digital and encrypted, nothing requires them to be as such, since all that's required is that they talk to the appropriate base unit. (And, apparently, the Sony headset you mention is also unencrypted analog as well.)

October 12, 2012 12:29 PM

I'd like to add to my previous comment; I checked with my neighbor and the phone I listened into was not digital, it was their cordless 2.4 ghzy phone. Sorry, it was not digital.

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