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I have a temperature alarm system in my office store room installed approximate 10 years ago by Siemens. This system gives a phone call to my mobile phone when the temperature goes above 25 degree Celsius. We have a dedicated land phone connection for this purpose. It stopped working a couple of days ago. I contacted Siemens, but they quoted me an unaffordable amount just for inspecting it (repair cost extra). So I want to repair it myself.

This system has an electronic mother board, which is connected to a modem (US robotics 56K message modem) through a 9 pin to 25 pin parallel cable (usually found in old printers). This modem is connected to a telephone line. I checked the telephone line with a normal phone and there is dial tone and I can make call from that (I have paid the bills). When I checked the modem all the lights are off. I planned to change the modem but shop keepers are telling me that this is model is discontinued and no longer available in the market. But one of the shop keepers told me that he can arrange it from abroad but for a very high price.

My question is that, do you think that simply changing the modem will help? Do modems need programming like we do with home internet routers? (If yes I can’t do it myself). Where do you think my mobile number is programmed? (on modem or on the Siemens controller).

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  • A specific brand and model of the modem would help identify whether the phone number could be stored in the modem. I suspect it is not and simply replacing the modem would resolve things. Have you check that power is getting to the modem?
    – wallyk
    Commented Aug 9, 2014 at 16:43
  • The modem is US Robotics 56K Message modem.support.usr.com/support/5668d/5668d-ug/main.htm
    – Jamsheer Moideen
    Commented Aug 10, 2014 at 16:21
  • This is electronics based and probably needs to be migrated.
    – The Evil Greebo
    Commented Aug 12, 2014 at 12:10
  • This question appears to be off-topic because it deals with systems installed in a business, and not a home.
    – Tester101
    Commented Aug 13, 2014 at 14:11
  • Dear All, Thank you all for your kind help. I could manage to buy a Dlink external serial modem for a reasonable price from local market, after searching for around 1 week. I simply replaced the modem, switched off the AC, waited for the temperature to go up, It is working!!!. I got call on my phone. As Mazura said, the controller has an interface to program the phone number. Thanks
    – Jamsheer Moideen
    Commented Aug 28, 2014 at 15:04

2 Answers 2

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If the modem is the only problem, replacing it might well solve the problem. As for finding a particular model of old modem at a non-outrageous price - ebay; sometime patience is needed for a very specific model or to get it at a non-absurd price, but generally modems are pretty cheap there.

Where the number is programmed - to be certain, you'd need a serial cable splitter so you can see what's going to the modem (connecting a computer so you can view the traffic between the modem and the controller.) Most likley it's in the controller, and a dialing command is being sent to the modem, but some fancier models of modem did have number-storage abilities, if I dimly recall the state of 15 years ago correctly.

You might very well find that you will be better able to solve the problem with a complete replacement using newer (and currently documented) hardware (telephone dialing temperature alarm or similar for a product search) rather than patching together old equipment - these things become obsolete, and one way to detect that is the absurdly high charge to even look at it.

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  • +1 for checking ebay for the modem - These became obsolete so fast there's a ton of NOS ones out there that people are dying to get rid of.
    – Comintern
    Commented Aug 9, 2014 at 4:50
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This for $30 may be worth a shot. I don't see an 1/8" jack, though. Check to see if it meets the version and protocol requirements of the control box. It's just a modem, the phone number was most likely input into the Siemens box if it has an interface (take a look inside if you must, carefully) or a device that was hooked to it. If you have multiple sensor locations not easily reinstalled, I would endeavor to keep it going as opposed to the $200 fix.

$200 solution, a modern stand alone unit. For multiple locations, the old sensor control wires (if they are the proper gauge) could be adapted to daisy-chain the phone line to the other locations to supply additional units.

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  • 1
    Dear All, Thank you all for your kind help. I could manage to buy a Dlink external serial modem for a reasonable price from local market, after searching for around 1 week. I simply replaced the modem, switched off the AC, waited for the temperature to go up, It is working!!!. I got call on my phone. As Mazura said, the controller has an interface to program the phone number. Thanks
    – Jamsheer Moideen
    Commented Aug 19, 2014 at 17:23

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