While I’m not writing this to inform you about ways to scare friends and family, the title could be true if the following idea was used in a sinister way.I am working on creating a very clever security system in my apartment. This is mostly for fun, but it does have practical applications. More on that when I spend more money on the project.

As a part of this security system, I want the ability to talk (or spook) to whoever is in my apartment. If I get a message that my door has been opened, I want to give the intruder the sense that there is someone around and completely aware of what is going on. There are other practical applications too, such as monitoring kids while you’re away to make sure they aren’t in a yelling match or make sure the babysitter isn’t being a bad example.

I figured the best way to provide an example of this was to show it in action. I have recorded a video which shows me calling a telephone number and Trixbox kicking into action. I will explain how this is done after the video:

So how does one pull off something like this? Well first you need to make sure that your Trixbox has an inbound telephone number (you can get a cheap 800 number from sites such as Vitelity) so that you can actually interact with your system. Once you have that figured out, you need to add a custom extension in the extensions_custom.conf file. An example entry would look something like this:

[custom-intercom]
exten => s,1,Set(__SIPADDHEADER=Call-Info: \;answer-after=0)
exten => s,2,Set(__ALERT_INFO=Auto Answer)
exten => s,3,Set(__SIP_URI_OPTIONS=intercom=true)
exten => s,4,ChanIsAvail(SIP/4587&SIP/9321,js)
exten => s,5,Macro(user-callerid,)
exten => s,6,Dial(Local/4587@from-internal,,A(beep),)
exten => s,105,Macro(vm,4587,BUSY)
exten => s,106,Wait(5)
exten => s,107,Macro(hangupcall,)
exten => s,hint,SIP/4587&SIP9321

In the above example (which was originally posted on the Trixbox forums by another user), 4587 is the extension I am calling and putting into speakerphone/intercom mode, while 9321 is the extension I am calling from.

After you have the code added to extensions_custom.conf, you must add a Custom Destination. If you were to use the above code, your custom destination would be something such as:

custom-intercom,s,1

Now you can finish up by adding a new inbound trunk and setting the Caller ID Number to your mobile phone number and setting the call destination to your new Custom Destination you just setup. This will make sure that calls will only go to intercom/speakerphone mode when you call and allow all other calls to route normally.

The above method is pretty secure unless someone figures out your mobile number and the phone number associated with Trixbox, as many VoIP services allow you to enter fake caller id information (which can be useful in the correct and honest conditions).

If you have questions or corrections to this entry, please let me know by leaving a comment. Also if you’re tempted to call the number listed in the video: I registered it for this video and it has since been decommissioned.