My cell phone is recording all phone calls (using Automatical Call Recorder on Android) and this has helped me a lot of times (both because I didn't hear something very clearly or as evidence for something).

Now I want to do the same for my landline phone (RJ11 connection, Belgian phone line). I have a Raspberry Pi 3 Mode B I received as a gift and haven't used yet. I was wondering if I could use my Raspberry Pi for this? In the ideal scenario it's recording all calls and storing them on my NAS.

I'm a programmer so if necessary I can code. I have little to none experience with building electronics.

Is this doable? If yes, where/how do I start?

  • 1
    Be very careful doing this. It's illegal, in some parts of the world, to record a phone conversation without informing the other party at the start of the call. You'll also need to edit your question (don't use comments) to provide the country you're working in - phone connectors can vary between regions.
    – goobering
    Jan 27, 2017 at 15:41
  • @goobering It's their own landline. I think it's cool. I also use the same app on my phone.
    – Aloha
    Jan 27, 2017 at 15:57
  • 1
    @PandaLion98 I enjoy a fine doodad as much as the next person. Sucks a little if you rely on the recording for something important and it lands you in court. Exercise a little caution is all - make sure you understand the rules for where you're recording.
    – goobering
    Jan 27, 2017 at 16:01
  • Just did some research on the laws regarding this in my country and as long as I'm one of the two parties in the call (so I'm not for example recording the calls my neighbor is making) there's no problem and the recordings can even be used in court as evidence (up to the judge if he uses it or not). So legally it's no problem. But after some Googling it sounds like this will technically be very hard.
    – Coder14
    Jan 27, 2017 at 22:05
  • @Lander Where you at?
    – Aloha
    Jan 28, 2017 at 2:47

1 Answer 1


My approach to this would be to do everything I possibly could to avoid interfacing the Pi directly with the phone line. It's definitely achievable, but it sounds a lot harder than I like my spare time.

Some Googling suggests that it shouldn't be too difficult or expensive to get hold of something that looks like this £16 adapter from Maplin. It accepts (I'm pretty sure) an RJ11 in from the phone socket, and outputs audio to a 3.5mm jack. That particular device, I note, is extremely badly reviewed - I suspect there may be better alternatives on Ebay.

Now you have to get the audio into the Pi. I'd recommend a USB soundcard.

Now all we have to do is listen to the audio input and trigger a recording if the incoming amplitude peaks over a threshold. There's currently a really good writeup on using SoX to do exactly this at pibat.afraidofsunlight.co.uk:

By specifying the right parameters to SoX’s silence command, sound can be monitored effectively trimming all noise until noise is detected, and then trim everything after so many seconds of silence.

This can be achieved with the following command:

rec - c1 -r 192000 record.wav silence 1 0.1 1% 1 5.0 1% : newfile : restart
  • I've bought this one: dx.com/en/p/… If it doesn't work, I haven't lost much money.
    – Coder14
    Jan 30, 2017 at 8:56
  • @Coder14 Did it work ?
    – Salah
    Sep 20, 2018 at 21:13
  • @Salah, sorry, moved on to other projects. Don',t really use my landline a lot anymore and I'm thinking to just cancel the service. So I can't tell you more if it works or not.
    – Coder14
    Sep 21, 2018 at 9:34

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