Added Siemens M20T GSM device

Siemens M20T

Siemens M20T

Last week i bought a Siemens M20T. The Siemens M20 Terminal is a GSM900 Phase II voice, data, group 3 fax and SMS terminal device. This device has been on my wish list for a long time. Although i had the ability to send SMS by using Voipbuster, using a dedicated device like the Siemens M20 has always been my favorite. Last week the Siemens M20T arrived and yesterday i took some time to do some tests. After making a straight 1:1 RS232 cable and inserting the new arrived SIM, i connected the M20T to my PC and switched on the power adapter. The LED kept on blinking, whereย  it should burn continuously. Of course, i had to enter the PIN code, so i started Hyperterminal and sent the appropriate command. So far so good.

Now it was time to test sending a SMS to my mobile phone. That wasn’t to hard, the command for sending a SMS is quite easy and human readable:

> TESTING 123<Ctrl+z>
+CMGS: 4

It worked. One problem though; the mobile phone displayed an error message saying the message could not be displayed? ๐Ÿ™ After some searching i found out that the text mode SMS i sent with the command above, is not supported by all mobile phones. However there’s another mode to send a SMS, called PDU mode. It involves a bit more work in encoding the SMS before it can be sent to the M20T, but i found enough documentation to send my first PDU-mode SMS after 2 hours. This worked well! ๐Ÿ™‚
The command for sending a PDU mode SMS looks like this:


The text sent is no longer human readable, the phone number is hard to recognize, but who cares if it’s working, as long as the M20T and my mobile phone understand it, it’s fine by me..

This evening i’ve started to write an interface to my Home Automation software so that i can send SMS messages whenever interesting things happen in and around my house.

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4 Responses to Added Siemens M20T GSM device

  1. Asif says:


    I read about the M20T above, I would like to knwo if this device can be used in M2M applications, primarily to send and receive commands to start or stop machines, send data from temperature/pressure sensors etc?
    I also read about Teltonika TBox20 pls advice if they have the similar features.
    Your info will be v imp for me.
    Thank You

    • admin says:

      Hi Asif,
      I’ve searched http://www/ for “TBox20”, but this search gave no results. Maybe it’s better if you read the manual of the Siemens M20T and decide for yourself if this device can do what you want…
      All i can tell you is that i can switch virtually anything in my house by sending an SMS from my mobile phone, so… all those things you mention should be possible with additional software etc. But if using a GSM terminal is the best way to do it in your case? I really don’t know… ๐Ÿ™‚

  2. kpan says:

    Hi Domotica,
    i’m trying to integrate my M20 terminal into my home net to use it for my Home-Automation-Notification-Services. HANS that’s sounds so typically german.

    I want to create an interface, like you’ve created for you home-automation. Can you please give more examples for using the M20 Terminal?

    Best regards,

    • admin says:

      Hi kpan,

      Interfacing with the M20 is quite easy to implement. Currently i use the following commands:
      – Echo off
      – Set PIN
      – PDU Mode
      – Send SMS
      – Read SMS
      – Delete SMS
      – Select Message Store

      That’s the basics you need for sending and receiving SMS. A sample pice of code for setting Echo off would look like this (Delphi):

      if WaitFor('OK'+CRLF,2000)
      then begin
      // success
      end else log('No OK after sending ECHO OFF (ATE0)');

      You’ll probably already have it but if not, here is the manual with all information you need to know to create your own interface.

      Good luck and feel free to contact me if you need more help,


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