I'm trying to do a C# code that call, through a 56k modem, a real phone number. The Call works correctly but now I need to know if the person I call answer to the phone or not (it is for an alarm project).

To do my call, I use AT commands. With a command like that :

ATD 00123456789;

I can process my call and it works good. But after that I have no feedback. And I need to know what's happened.

When I have searched in Google, I found na AT Command :


that supposed to list the current call.. http://www.g1sat.com/files/HNS_9201_AT_Reference.htm#AT_plusCLCC
But for me it doesn't work.. The return is always ERROR.

If someone has an idea thanks for your help.

For Info my 56k modem is an 3Com U.S. Robotics, and my c# code use the ActiveComport Serial Port Toolkit.

5 Years
Discussion Span
Last Post by debraph

These are for GSM (cellular) modems, I think.... They may not be supported by your modem. You might want to check if your modem has an extended command set that supports what you're trying to do.


How do analog phone lines know when someone has picked up? Seeing as they only use 2 wires (sig and ground) there are no control signals for things like picking up a phone. I suppose it can be determined based on the frequency (if the prominent frequency does not conform to a DTMF signal then assume its picked up). I bet anything that's based on digital technology (VoiP, GSM, digital phones) would have such a signal. I am no expert on the subject but used to do a bit of telecom for work.

I would sugguest that in the phone message you send out to have the call receiver press a button on the phone to confirm they are human (not that this couldn't be fooled by a machine). If they don't hit the button in set time frame assume they didn't pick up.

Edited by skatamatic: n/a


I am not too sure how the word 'message' got made into a spam link... and now it is too late to edit it. My appologies.


Thank you skatamatic for your answer. I think will think about a kind of solution where the person have to push a button to "send a receipt".

I will also try tomorrow to work with a GSM Modem, to have more awareness about the context of the line.

I will post later if I find an interesting solution.

Thanks all.


So ... Finally I have installed a GSM Modem and now I'm able to send a


command. With that I can have knowledge about the list of the current call.

It works find for my alarm system. Thanks all.

See you.

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