I was hoping to create a cheap security system by connecting an Arduino to the phone line output of a base station.

Since the base station should call a phone number if the alarm is tripped I wouldn't have to do much hardware hacking so long as I can read/parse the output from the base station.

My question is can I read serial output from a phone line like this?

  • 1
    Serial connection over a phone line is done using a "modem" - you can probably still find an RS232 external one on a surplus site for which you will need a serial level shifter (with implicit inversion). You may also be able to find a new module for embedded use, perhaps even one with logic level serial. Most sophisticated enough to use the AT command set can dial. Commented Jan 2, 2015 at 15:01
  • These days you can find TTL modems, removing the need to deal with RS-232. Commented Jan 2, 2015 at 17:16

1 Answer 1


Phone lines run off of the RS-232 telecommunications protocol which can run off -25v to 25v, which would completely destroy your Arduino. Luckily there is an IC made to help you with that. You can use the MAX3232 IC to convert RS-232 to TTL 5v or 3.3v (Same chip can do either). Look at providers like Digikey for just the chip or you can get a breakout from providers like SparkFun.

TL;DR Yes, but you need a special IC to not fry your Arduino.

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