>
>
>>>Most simpler systems dial into the center and send DTMF codes. One can 
>>>program just about anything to be sent.
>>>
>>>Peter
>>>
>>>      
>>>
>>Although many proprietary alarm protocols have come and mostly gone, the 
>>three most popular remaining are 4x2, Ademco Contact  ID and SIA protocols.
>>
>>4x2 uses pulsed tones to send 4 (account number) and 2 (alarm signal) hex 
>>digits at 10, 20 or 40 pps.
>>Ademco Contact ID sends 15 (information) and 1(checksum) DTMF digits 
>>representing account number, event code and zone number etc.
>>    
>>
>
>What I meant was, you get to calculate the messages yourself, and store 
>them if you want it to be compatible. I also think that the Contact ID 
>requires some special tones which cannot be made with a regular DTMF 
>(and which are not issued by the cheap alarm dialers I alluded to).
>
>Peter
>  
>
Calculating the message yourself is one of the greatest errors you can 
make with a security system.
That was the greatest downfall of the 4x2 format, 2 hex digits available 
to identify alarm type (burg, fire etc) and zone (front door, hall way 
etc). Since there was only a pseudo standard for what hex digits mean 
what, communication of meanings at the time of install between the 
installer of the security system and the central station doing  the 
monitoring was of tantamount importance. Unfortunately this didn't 
happen in a large amount of cases.

The industry eventually realized this and created contact id and sia 
standards. Each of these standards send a unique signal type (Burg, Fire 
etc.) and Zone Number for the zones that are violated at the time of the 
alarm.

When sending Contact ID, the alarm transmitter does listen for a 
particular handshake tone (that is not DTMF) from the receiver, once it 
is detected all transmittion from the sender to receiver is in standard 
"DTMF" that any receiver that adheres to telco DTMF will understand.

I can send a properly formatted Contact ID signal to a regular Central 
Station Alarm Receiver using a normal modem.
No special tones involved other than the tones the CS receiver sends for 
handshake/kissoff. The CS Receiver will not know the difference if it 
received an alarm from an alarm system or from my modem.

Randy
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