Alarm System Interrupting DSL Internet Service, and a Fix

August 6, 2008

When I moved into our new house earlier this year, we immediately ordered high-speed DSL Internet service from Verizon. In addition, we installed a security system via a Monitronics contractor. While Scott, the Monitronics contractor, was installing the alarm box and hooking it up to a phone line, I asked him if there should be a DSL filter as well. He explained that the alarm system would only actually use the phone line during emergencies, and that it would work without a DSL filter anyway. I took his explanation at face value, and he hooked up the alarm system without using a DSL line.

In the months since then, we’d been having trouble with our high-speed Internet service. It’d shut down / cut out several times a day, mostly at inappropriate times especially during important videophone conversations. At other times, it’d slow down to a trickle and our pages would l-o-a-d o-h s-o s-l-o-w-l-y … I kept trying different things to fix this problem — calling Verizon, paying $$ for a new wifi router, paying more $$ for an all-in-one modem/router from Verizon, shortening the phone / cable lines, tweaking router settings, etc etc etc. Nothing seemed to remedy the DSL service problems, which was quite embarassing to me — after all, I’m a Proud Geek who prides myself on my ability to solve computer and network problems!

Then I had a brain fart, ahem, notion: what if the alarm system was indeed interfering with our high-speed Internet service? After all, it was installed without a DSL filter. So, I emailed Scott and asked him to come and install a DSL filter (that we already had from Verizon) between the alarm system and the phone line. Despite protestations that the alarm system is NOT interfering with our DSL service, he came the next day, charged us $85 (sigh), installed the DSL filter in minutes, and left.

And behold and lo, our Internet service has (miraculously?) improved! It has not shut down even once in the week since Scott’s visit — even during ultra-important and lengthy videophone conversations. Connection stays swimmingly high, and our pages load quickly and consistently. YAY! My Proud Geek reputation stays untarnished!

Moral of the story? Don’t listen when alarm technicians tell you that alarm systems don’t need a DSL filter. If you get DSL high-speed Internet service, insist that alarm technicians do plug alarm systems into a DSL filter then into the phone system.

What are DSL filters, and why do we need them? High-speed DSL service uses the same phone line we use. These phone lines (mostly) have 4 “wires” within each phone cable. (Office phone lines often have six wires for additional phone functions like intercom, conferencing, etc — that’s why office phone lines are sometimes thicker.) DSL service uses two of these wires and voice service uses the other two wires. But when regular telephones are plugged into a phone line that is being shared with DSL service, users can hear an electronic “hiss.” In addition, DSL Internet service users may see interruptions. DSL filters are used in between telephones and phone lines to make sure that telephones use the two wires that aren’t being used by the DSL high-speed Internet service.

As an aside: we had our Monitronics alarm system installed for free, including numerous wireless window sensors, a motion detector, two strobe lights, and an alarm console. We pay $38 a month. If we get several referrals (maybe 2? maybe 4?) of people who then use Monitronic’s alarm system, our first year’s payments are waived. If we get a few more referrals (2 more? 4 more?) after that, then payments for the following year are also waived. If you’re interested in getting the same deal and would like to be one of my referrals (and then you could work on getting your own referrals), email me at with “Monitronics” in the subject. I don’t get paid nor get advertising dollars for doing this blog, so I’d consider this semi-payment! :-)


34 Responses to “Alarm System Interrupting DSL Internet Service, and a Fix”

  1. queenalpo Says:

    We don’t have an alarm system, but we do have lighted doorbells that go off whenever our neighbors hit the button on their keychains to unlock their car.

    Don’t ask how long it took us to figure THAT one out. Suggestions?

  2. proudgeek Says:

    Does your doorbell system have tiny switches that you can adjust? If so, try changing the switch settings on the transmitter, and do exactly the same changes / settings on the receivers.

  3. H Says:

    I could give you dsl filters for free. I got them from Qwest when I ordered HSI package. I do not have alarm system so they are not needed for my computer.

  4. Bryan Says:

    Good article – with one correction.

    The DSL goes over the same pair of wires that the voice does. It’s not over separate pairs.

    There’s some good articles about the different frequencies that analogue uses versus digital.

    Thanks again.

  5. Dennis Lee Says:

    Yes I also discovered the same problem as you did as well.

    I opened the security alarm panel and discovered an RJ-31 connector plug and basically custom pigtailed out my own leads to a DSL filter.

    It was a little tricky decoding the colored wires so I had to use an continutity tester/multimeter to confirm color coded connections between the security alarm panel and RJ-31 jack to create an equivalency conversion table for wiring out the custom pigtailed harness that would silence that interminable alarm’s message “Protest” and incessant beeping.

    Basically this is the short story version of a long trial and error process:

    From left to right phone connection is:


    Taking connection and finding the equivalent connections is:

    Black —–> Gray (different)
    Red ——-> Red (same)
    Green ——> Green (same)
    Yellow ——> Brown (different)

    Once I wired up the above associated color wired combinations (careful the wires are ultra thin tricky to work with) and soldered them up using a cut in half telephone line cord with RJ-11 plugs on end I was set to test.

    I used a RJ-11 line coupler to join the two pigtail seperate pieces (one to connect to the security alarm panel side (grey, red, green, brown) and the other custom pigtail piece to connect to the other old security alarm cabling going back to phone connection (black, red, green, yellow) side.

    I held my breath after all this trial and error measurement and custom pigtail harness making work- hoping it would work the first time out- hoping for uber geek success and luck.

    Voila, I had the security alarm fooled and instead of the alarm displaying the previous “Protest” message and all the incessant beeping it said “Away” and started beeping instead an “Exit” before arming alarm.

    Another invaluable uber Geek lesson learned via real life technical trial and error and my techincal uber geek reputation reclaimed for solving technical computer and networking problems and also as well fixing alarm technician and electronics technician problems as well.

    Well in this case I saved myself the $85 dollars, had the work done in about three hours, and saved myself from having to talk to less than enthusiastic alarm technician and request the additional work order.

    More importantly, now I have taught myself and now know how to fix unanticipated and unforseen additional technical computer/security alarm/electronics technician problems as an added dividend and bonus as well

    Additionally, I can also as well now post on a prospective tecnhical resume; as a very surreal real life technical problem solving case study and how it was successfully resolved using learned and applied technical troubleshooting techniques and procedures in an given competitive job interview situation.

    It’s a very satisfying feeling to now know this most recent and challenging technical problem was resolvable after all and not as bad as I had first envisioned and imagined. One of the necessary steps of course was tracing out the line connections between the security alarm box/panel and phone lines to do the inital survey and information collecting. So evaluate and plan your own problem solving situation before attempting to tackle the problem head on as you will need some basic electronics tools to facilitate the repair/upgrade as explained above.

  6. proudgeek Says:

    Wow, Dennis! Thanks for the explanation / comment.

  7. K. Ya Says:

    We don’t use our alarm and have never had any problems with the phone line or our adsl connection until the other day when we came home and the alarm was beeping, not the siren, just the keypad. I managed to make it stop but the service light is still on and the damn thing won’t stop ringing our phone line, making it unusable. Good thing we have VOIP too. I have tried many things as our internet connection was affected as well, but after fiddling around in the alarm box I have managed to get adsl back online. We still have no phone and the security firm who installed the alarm has not responded to my email. Probably because we are not paying them. Haha.

    Any advice would be greatly appreciated. There is no filter on the alarm line, when I put one on the ringing stopped but there was still no dial tone and the modem drops out. The modem works fine when the phone line in the alarm box is disconnected.


  8. jacob Says:

    We have cable telephony and internet – could our alarm system be interfering with our phone system – we often hear clicks when talking on the phone, and lose connection for a second – could that be the alarm doing some kind of scheduled dialer test?

  9. Bob Says:

    A tech at my alarm monitoring company told me that the regular DSL filters are not what you want for your alarm system. You want an Alarm DSL filter. He recommended the Home Security Store (they’re about $19).

  10. Bill Says:

    Wow! Awesome detective work!

    Thanks for solving the issue and not throwing Monitronics under the bus in the process!


    We’ll try to insure our technicians are better-educated about possible interference issues such as this in the future. Though, installers are actually all independent of our company as employees of authorized resellers, so some are a little variable in how well they train their staff.

    I actually have Verizon internet service at my home as well, and have seen a few different things such as my alarm signals which can mess up service.

    Again, thanks for patiently resolving this at your end and providing the description for others’ benefit!

  11. DSL Filters Says:

    Excelsus makes filters specifically for alarm systems – Excelsus Z-A431PJ31X DSL alarm filter. A regular DSL filter will not work and could/would interfere with your alarm system. Always talk to or have a technician from your alarm service when servicing your system

  12. For those of you wanting to use a standard DSL filter I thought I’d give you a bit of info. Alrm panels use what is called a RJ-31x jack rather thatn the standard RJ-45 (Ethernet) jack to connect a phone line (at least if they follwed set standards when they installed it. The difference is that of the 8 positions available in an RJ-45 only 4 are used and they are the outermost pair and the inner most pair. An alarm panel must have the ability to overide any phone calls being made at the time of the alarm. So how this is managed is the phone line coming into the house use position 3&4 (innermost pair) and then sends the phone line back out on the outermost pair of wires 1&8. that way, the panel can hang up, make its call and then reconnect your line. Anyone needing more info can hollar at me at

  13. To be more clear, you can buy a Alarm panel DSL filter which does this or you can place a standard DSL filter on both the incoming and outgoing lines of your panel. Since this is essentially what an alarm DSL filter does.

  14. Sergei Says:

    Thank you for the good suggestion. I have the same problem with my DSL service. When I installed the filter at the alarm the DSL service improved, but the dial tone in the phone line disappeared!What should I do? Please help! I have five telephone jacks, including alarm.

    • proudgeek Says:

      I don’t have a good answer, except to perhaps try installing the dsl filter at each telephone jack not being used for DSL …

  15. Josh Says:

    The ONLY colored wires that matter on a phone line is the red and green (tip and ring) those of you who have altered your alarm systems because of the dsl issue will have a rude awakening when your alarm system fails to call for help. The alarm system sees the voltage on the line and thats why the protest indicator goes away.
    If one was to look at a “D MARK” the green box in your yard or your neighbors yard tha belongs to the phone company and trace the wire fromyour house to it, you would find only 1 pair of wires 2 wires total feeding your house, even if you have 10 jacks in your house. that dial tone only comes from a single pair of wires from the “D MARK”
    The rj 31x jack will sieze the line in order to call out to monitring station. the house line comes into the Rj31x and out to the panel on the grey and brown, SO when the panel is in trouble or sences an alarm the relay clicks and takes over the phone line and calls
    for help, whether you are on the phone, online, or what have you.

    Whats more important? Your phone call? Your Download? Or Your life??
    When people begin to tinker with things they think they understand is when dangerous things happen!!!
    The thickness or wire count has NOTHING to do with dial tone.
    6 conductor wire is ethernet cable or cat 5, but can and will be used as phone wire. phone wire cat 3 is a 4 conductor. but only needs 2 conductors for dial tone. the cat 3 and cat 5 is the distinction on how tightly the pairs are twisted. Data communication works better the tighter the pairs are twisted together.

    If you have made alterations to your system that prevent phone line seisure you will not get a response from the authorities because the Alarm panel will be unable to call for help!!! Usually any installer worth their salt will set the alarm to call out in the early am, for its daily test, Yes even when there is no “emergency” the alarm panel calls out to the central station.
    This is a very important function of the Alarm System.
    Any one using a digital phone service (VOIP) can expect to have problems with their alarm panels. in most cases a gsm radio is added for the Alarm Panel so it is able to make that call.
    If your installer or sales person failed to ask the simple question, ” do you have digital phones?” you may want to look at a different company!
    If anyone needs any help Please feel free to ask,I am an Alarm and Security Technician with 15 years in the field experience.

    • Tony Says:

      Hi Josh
      I have an alarm system and my phone line disconnects several times a day. My phone is a cable line with a modem at entry point incuding my internet and tv. If I install a filter will it resolve the issue, and what type of filter should i install.

    • Stephanie Nguyen Says:

      Hi Josh
      I’m having problem with my alarm system after having DSL Internet installed. The phone line dropped or no line at all several times a day. I have DMP XT30/XT50 security system and it is just 1 year and 10 month old. The Fire & Security company charges me more than $520.0 to have the techs come to my house for troubleshooting but the problem is still happening. They told me to buy an alarm DSL filter – model RJ31/38X. I bought one at Ebay but it doesn’t work then the alarm people give me a similar one but I installed to the panel as the way the tech told us but the alarm monitoring people still don’t receive signal from us. The techs said the incoming and outgoing lines are fine when they were testing. I don’t know if I have to call the CenturyLink to cancel the internet service so the alarm would work fine as before. Please help what we should do besides intalling and call the operator for testing.
      Thanks a lot

      • proudgeek Says:

        Make sure ALL phone lines – except the DSL line – have this filter. Make sure the alarm’s phone line has this filter too. I got a bunch of filters from the DSL (Verizon) company, and that did the trick.

  16. Stephanie Says:

    I have 5 phones in the house, should every single of them have the DSL filter installed? This filter is 4 pins only not like the Alarm DSL filter with 8 pins. Do you think it should work? Thanks a lot

    • proudgeek Says:

      Why not give it a try – ALL phones (including the alarm’s line) must have these filters where they meet the wall jacks. Only the DSL line should not have this filter. I’m pretty sure you can get extra filters from the DSL company.

      • Stephanie Says:

        I believe there is a filter at the modem where they split the phone line to 2 jacks, one for phone and one for internet. The tech is at my house now and he got a hard time to figure out as well. I told my son takes off all the phones which do not have filter so I hope this will work. Thanks a lot for your help. I do appreciate you. I will let you know if it works.

      • proudgeek Says:

        Hope it works! Keep us posted, please.

  17. Stephanie Says:

    The alarm people said we will need a fax quality speed line upgraded because the voltage drops from 48.8 to 3.2 when the alarm panel trying to send a signal and it needs at least 6+ VDC. I don’t know what VDC means. I called the internet and they said they will need to slow down our internet speed (currently is 12M) to see if the alarm will work if not then I have to call back to talk with the business office. Oh my god! it is a hassle. I think I have to cancel the internet service provided from CenturyLink because they use one phone line for everything and it messed up the alarm system. Thanks

  18. Stephanie Says:

    I will keep you updated after all. I will have to wait for 24 hours to see if lowering the internet speed will make it works. It is weird really. Thanks for all your help and thanks for the wish.

  19. Stephanie Says:

    The alarm is still not working after internet speed reduced. I called the internet people and a tech came to my house this morning. He did the testing for voltage and it is fine. I was on the phone with the internet retentiong dept. for 3 hours yesterday and they told me that we will need phone and internet lines separately so they will not interfere with each other. I had the alarm and internet teches talking with each other and one blames on the other and I’m in the middle of everything and the problem is not solved yet. I requested to turn off the Internet temporarily to test if the alarm worked as before but the tech refused. Finally the customer service asked me to pay extra $5.00/a month to have another separate line completely for the DSL. I hope this will solve the issue but not sure yet until it is done. The internet tech said he has been working for this job for 15 years and never knows that the DSL creates Alarm fails even there are filters as you knew. I asked why the alarm worked fine before when we had the internet with Comcast. He couldn’t answer and continued blaming on the alarm panel. It is kind of a mess now. Please wish me luck.

    • proudgeek Says:

      Oh no! I’m sorry to hear about all this! Wish you could cancel everything, do one, see if it works , then add the other.

      • Stephanie Says:

        I wish I could cancel the internet service but it has been 6 months and still have 18 months to go. I didn’t notice that the alarm fails until about a month ago. They didn’t let me to cancel internet withou pernalty because they said the problem is not on their side but the alarm people. Moreove switch the service is costly as well. I bought brand new modem from CenturyLink $99.99 and paid 99.99 for running a line to my office so the initial fee plus tax is more than $200.00. The alarm people charged me $520 for coming out to look at the panel. Oh my god I go crazy with this really.

      • proudgeek Says:

        $520!! I feel bad for you. Hang in there …

  20. Stephanie Says:

    If the issue wouldn’t be solved and I end up with many bills from two to them, then I think I have to file a complaint with BBB. Please give me advice.

    • proudgeek Says:

      Yes, BBB is definitely a good resource. You can check online and look up a company’s history with complaints, and you can add your own complaint online.

  21. James Says:

    Hi there, personally i have to admire this article’s writer. It really helps my half month depresson of ADSL slow in speed. I was suffering half month with opening a webpage takes 5mins, download speed avg 10~20kps. After read this article, i tried to open my alarm box and plug in a filter, then speed suddenly jumps up to 400~500kps. What a good sharing! Now i am more than happier to tell everyone, it really works! Appreciated this writer’s generous sharing. Cheers/James

  22. “A regular DSL filter will not work and could/would interfere with your alarm system.”

    I use a regular DSL filter. In fact, I use two. The house phones run from one. The alarm runs from another. They cannot/do not interfere with my alarm system.

    Inside my alarm panel I fitted a conventional telephone socket end (a type 600 in my case as I’m in the UK) to the telephone cable. The filter plugs into this. Into the filtered output a 431A plug with a short length of cable (proper copper, not tinsel wire) is fitted and that goes to the alarm communicator.

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