Electronic Alarms and Home Security Devices - Do-It-Yourself Security Alarm Resources
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alarmtexpert
12-30-05, 08:32 PM
I purchased a Napco Gemini 1632 security control to upgrade a non-working system in a house I recently bought. The phone line on the outside of my home is in a very vulnerable place so I did some research about how to monitor the status of the phone line.
The first thing I did was start researching all of the places where a home owner can find support without having to hire a security company. I figure I might as well learn as much as I can so I can is tell if my system is working correctly.
One of the resources I found explained about turning on TLM (Telephone Line Monitoring) in the programming. The problem is everytime I program it this way the alarm system intermittenly has false alarms. I bought a book called The Key To Your Security System from SecurityForYourHomeland.com and I'm beginning to think I've been misdirected about telephone line monitoring.
My telephone always works, why would the alarm be going off?
The first thing I did was start researching all of the places where a home owner can find support without having to hire a security company. I figure I might as well learn as much as I can so I can is tell if my system is working correctly.
One of the resources I found explained about turning on TLM (Telephone Line Monitoring) in the programming. The problem is everytime I program it this way the alarm system intermittenly has false alarms. I bought a book called The Key To Your Security System from SecurityForYourHomeland.com and I'm beginning to think I've been misdirected about telephone line monitoring.
My telephone always works, why would the alarm be going off?
MrRonFL
12-30-05, 09:15 PM
The TLM feature works by monitoring the line voltage supplied by the Telco. If you are far enough from the central switch, or the local switching equipment is getting long in the tooth, during certain peak periods, the voltage may drop below the detection threshold set in the system.
If you are truely worried about line tampering, you can do something like putting the demarc in a cabinet with a tamper contact on the door. In truth, the kind of theif that knows enough to tamper the phone line is going to give the average home security setup a real run for the money. Happily, such burglers are generally pretty rare. 99% find the presence of a security system to be incentive to move on to an easier target.
If you are truely worried about line tampering, you can do something like putting the demarc in a cabinet with a tamper contact on the door. In truth, the kind of theif that knows enough to tamper the phone line is going to give the average home security setup a real run for the money. Happily, such burglers are generally pretty rare. 99% find the presence of a security system to be incentive to move on to an easier target.
alarmtexpert
12-30-05, 09:24 PM
Well that's what the guy at SecurityForYourHomeland.com told me as well but does that mean I am not able to use the TLM feature of the security panel? Quiite frankly I decided to try this forum because I thought he didn't know how to fix the problem so he just told me what you told me to keep from having to continue to troubleshoot it.
The guy at SecurityForYourHomeland.com told me to use a meter to check the voltage on the phone line which I did. It was 48 volts but I have not found out yet what it should be. So should I just blow it off?
The guy at SecurityForYourHomeland.com told me to use a meter to check the voltage on the phone line which I did. It was 48 volts but I have not found out yet what it should be. So should I just blow it off?
MrRonFL
12-31-05, 09:47 AM
The issue is voltage drop, which is a combination of the resistance of the physical wires from the Telco switch to the end users, and equipment in their homes. A typical home will support about 20-25 REN (ringer equivalent number, which is marked on every device that can plug into a phone line; you add them up).
As more users load the phone network at peak times, the voltage can drop below the 30-35 volt threshold that most of the TLM features are set to trigger at. A household phone is pretty simple, and will function at around 20 something volts. 48volts is about typical.
The other factor that can happen is if you have a skinned wire exposed to the weather, or a phone pedistal near by that's exposed to water infiltration, it can also make the phone lines act flakey. (I once had a situation where the client had phones cut out at the same time every day. They thought the alarm system was grabbing the line. It turned out that their automatic sprinklers were turning on and drenching their NID...)
As more users load the phone network at peak times, the voltage can drop below the 30-35 volt threshold that most of the TLM features are set to trigger at. A household phone is pretty simple, and will function at around 20 something volts. 48volts is about typical.
The other factor that can happen is if you have a skinned wire exposed to the weather, or a phone pedistal near by that's exposed to water infiltration, it can also make the phone lines act flakey. (I once had a situation where the client had phones cut out at the same time every day. They thought the alarm system was grabbing the line. It turned out that their automatic sprinklers were turning on and drenching their NID...)