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I would like to do a DIY intrusion detection system. I think I understand roughly what it's needed (door magnetic switches, windows magnetic switches, IR motion detection, password prompt, webcam), though I'd like to know how you can actually call the police.

I saw the "ITEAD SIM900 GPRS/GSM minimum system module" in my local retailer's store and I find the price pretty interesting (~ 45$). This would however "only" allow me to send SMS to a mobile phone when there's an emergency, not being able to directly call the police isn't so good. What do they mean by "It can communicate with controllers via AT commands (GSM 07.07 ,07.05 and SIMCOM enhanced AT Commands)."? Do I need an external phone? I though I could directly interface this module to a MCU.

Another possible solution might be to set up a raspberry pi with GNU/Linux + gammu and an attached (compatible) mobile phone and send SMS to a mobile phone. No possibility to contact the police though.

Basically with either solutions IMHO I could send an SMS to myself / my friends when there's an intrusion and relay the message to the police. It's not a so good solution though, because with all delays summed up the thief may already be gone.

Landline phone wouldn't be a good idea either, since with cable TV/Phone/Internet isn't that reliable at my place. I though I'd pre-register an audio message and play it from one speaker if I can manage to force a phone to call a given number (which could be done with AT commands, theoretically).

What would you reccomend / do?

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  • \$\begingroup\$ well, I would do that if I get an answer that can solve my problem. Most of the times it's unfortunately not like that. Anyway I always upvote all answers, because I feel that even if it doesn't solve my problem, it helps me in some other way and that person has been willingly to offer some of his time in order to reply to me. \$\endgroup\$ – user51166 Aug 27 '12 at 10:34
  • \$\begingroup\$ You got a very adequate set of answers for eg this question. Telling Olin that his time spent on you is liable to be wasted is liable to achieve a very positive result - but probably not one you desire. Rejecting PICs for the reason you do seems unsound [tm] | Try agaim. Hmmm Olin again - sole answer and YOU say it is good - but still no Cookie. Time, I think, to find out where the accept button is. \$\endgroup\$ – Russell McMahon Aug 27 '12 at 11:17
  • \$\begingroup\$ @RussellMcMahon: if I receive a set of good answers, how do you mark just one as the accepted without being rude to the other who answered? On second review I accepted Olin's answers, but that doesn't mean that other people's answers were no good (they were useful as well)! \$\endgroup\$ – user51166 Aug 27 '12 at 11:34
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    \$\begingroup\$ You can't really win :-) - but it's a good idea to try. Some people place considerable value on getting feedback for good answers and may not be inclined to answer if a person often accepts no answer - or so they tell me. Conversely, some people are not keen to answer once an answer has been accepted, You can change the accepted answer after the event fwiw. \$\endgroup\$ – Russell McMahon Aug 27 '12 at 13:49
  • \$\begingroup\$ You mention calling the police. What should it be capable of doing then? Voice syntezing or just playing a sound from a sound source (that is outside this component)? (also just a hint: make sure you are allowed to hook up a alarm directly to the police - here in Sweden that is not allowed) \$\endgroup\$ – Jontas Aug 27 '12 at 14:12
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Arduino announced a GSM/GPRS shield (see also here) recently. I have no experience how it works, but I guess it's worth a look.

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  • \$\begingroup\$ Interesting. It explicitly states it can do voice calls. That seems good (if true). \$\endgroup\$ – user51166 Aug 27 '12 at 14:16
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If you look for a device to hook up and call a phone number and play sounds from a sound source there are a number of other modules that will do this for you, look up for instance "Siemens MC46" or a TC35 with a voice adapter - when I look quickly at ebay there are a few alternatives that all support voice calls.

What I call sound source can be anything, a sound card, voice synteziser and old casset deck - just anything that gives the message you wish to send. And the reason I think this is needed is since the examples I gave all just have a audio in pin or other connector.

That the device you have supports AT commands is a way of telling you how to communicate with it (for instance how to send a SMS)

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  • \$\begingroup\$ If a device supports AT commands does it also support outbond calls? \$\endgroup\$ – user51166 Aug 27 '12 at 14:25
  • \$\begingroup\$ AT commands is not a way to say voice calls. To quote from the link "The [AT] command set consists of a series of short text strings which combine together to produce complete commands for operations such as dialing, hanging up, and changing the parameters of the connection." \$\endgroup\$ – Jontas Aug 27 '12 at 16:16

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