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Alarm Switch Troubleshooting

Finding and Fixing Lightning Damaged Alarm Contacts

Most magnetic switch troubleshooting jobs involve fixing hardwire contacts that are an open circuit, either all of the time or intermittently. This page deals with the opposite condition: A switch that is always closed, regardless of the position of the door or window where it’s installed.



Although alarm system contacts that have failed closed or are welded closed are much more rare than the open variety, they do happen. If you notice a door or window that doesn’t seem to “trip” the alarm when it’s opened, this page is for you.



For help with always-open switches and faulted zone problems, see my main “Burglar Alarm System Troubleshooting” page.


For alarm contacts that are intermittent and/or falsing, see “How to Troubleshoot Alarm Panel Wiring.”



Causes of Welded Alarm Switches


The most common cause for an always-closed alarm contact is a nearby lightning strike. While a switch may occasionally fail in the closed position due to wear and tear, damage by lightning is most often the cause.


Lightning strike over Chandler, AZ


Lightning doesn’t have to strike a house directly to cause this damage. In fact, I've found welded contacts in many homes where the owner had no idea anything was wrong (another good reason to test your system regularly).


When lightning discharges, either from cloud-to-ground or cloud-to-cloud, an enormous amount of electrical energy is released. This huge current generates an electromagnetic field that induces voltage and current in any nearby conductors, including house electrical and alarm system wiring of all types.


These currents are often many times greater than the wiring and connected devices were ever designed for. Excess current can easily fry appliances and electronics, including alarm equipment.



Modern alarm panels often have lightning protection features built-in to minimize the chances of induced voltage entering the circuit board through the field wiring. These can include circuit grounding, spark gaps, MOV’s (metal oxide varistors), and other surge arrestors. The idea is to block or dissipate to ground any voltage spikes that travel through alarm wiring to the screw terminals, before they reach the sensitive components.


Spark gap in action (Link to YouTube video)



The hardwired magnetic contacts on the doors and windows aren’t nearly so lucky. They are simple magnetic reed switches, connected directly to the security alarm wiring with no means to prevent lightning damage. Any large surge of current will flow directly through a closed contact, and can easily heat it enough to weld it in the closed position.



In case you’re wondering, plugging the alarm system’s low-voltage transformer into a surge protector will not protect the switches, but it could help save the transformer and circuit board.



Lightning hitting at a distance may not do any harm at all, while closer strikes may be arrested by the protective devices on the alarm circuit board. Lightning that occurs very nearby can blast through even the best protective measures and vaporize components. Depending on the extent of the damage, the entire system may need to be replaced (more on that later.)


Lightning hitting a neighborhood

For now, let’s assume that you don’t have smoke billowing from your alarm panel, but you do have a switch that doesn’t seem to be tripping the keypad chime or display when opened.


Welded Switch Troubleshooting Guidelines


Verifying a Frozen or Welded Alarm Switch


While a switch may appear to be welded or unresponsive, it’s a good idea to make sure. If several openings are tied to a single zone, the zone will show faulted when any one of the openings is faulted. This can make a switch appear to be unresponsive, when it’s simply on a zone that’s already tripped by another opening.


A zone list is an important switch troubleshooting tool. This shows which doors, windows, motion detectors, and other sensors are tied to which panel zones.


Over time, we can lose track of exactly which zones connect to what. Heck, I installed my entire system myself, but I can't remember every zone location without the zone list!


Alarm panel zone list for a DSC Power 832 with 16 zonesAlarm panel zone list on paper. Even a basic list like this one makes switch troubleshooting much easier.



If you’re not very familiar with the zone layout of your alarm system, check your Owner’s Manual for a zone list. It should show which door and window openings are connected to each alarm panel zone number.


This information may also be listed inside the main panel box lid. If your system is monitored, contact your alarm monitoring company for a zone list.


Zone list written inside lid of an Ademco Vista 10SE using 3 of its 6 available zonesZone list hastily written inside panel lid (Not my work). This is for an Ademco Vista 10SE using 3 of its available 6 zones (It was installed in an office suite)

Zone 10 "F D" is Front Door

Zone 11 "Motion" is Motion Detector

Zone 12 "Pendit" is Wireless Pendant Transmitter, probably for use as a panic button



If you don’t have a zone list, now may be a good time to make one. It’s easy to do, and will come in handy for any future switch troubleshooting. Here’s the procedure:

  1. Close all exterior windows and doors so that the keypad shows “Ready”
  2. Open each door and window, one by one, and check the keypad to see which zone is displayed as faulted/open
  3. Write down which zone is tripped by each opening. When you’ve checked every opening, you’ll have a complete zone list
  4. If opening a contact doesn’t kill the “ready” condition, that is a problem switch


After you’ve verified your zones and you are sure a switch is not showing up on the keypads when in the open position, move to the next step.


You can download and print out a FREE copy of my Basic Alarm Zone List to use as a fill-in form to make this easier.

It has 28 lines for alarm zone information, including zone numbers, descriptions of protected areas, loop and serial numbers, and more.


Download a FREE copy of my Alarm Installation Record Sheet.

This has spaces to enter a homeowner or business name, address, phone numbers, and panel make and model details. The lower portion of the form is a shorter, 20-zone version of the Basic Alarm Zone List above.


Each of these PDF documents will print out as a single 8-1/2 x 11 page, and I created them both to work with any type of alarm panel - wireless, hardwired, or hybrid.


Freeing-Up Frozen Alarm Contacts

Begin your switch troubleshooting by locating some sort of tool you can use to tap on the problem switch. The handle-end of a screwdriver works well. You can also use the handle of a wooden spoon or a short wooden stick.


Screwdriver handle can be used to smack switches“High-tech” tool for breaking welded magnetic contacts loose


Next, turn on the system’s “Chime” or “Watch Tone” function. Most all alarm systems have this feature, and it works as a great switch troubleshooting tool. (If you don’t know how to activate the chime, or if you’re not sure your system has this feature, click here for help finding a user manual)








An alternative to the chime method is to have a helper watch the keypad display, and call out when they notice a zone fault. If your home is very large, or if the problem zone is far from a keypad, you can communicate by cell phone.


Hardwire contacts - Recessed


Next, go to the alarm switch in question. Tap the problem switch lightly a few times with the your trusty screwdriver handle or other high-tech tool of choice. If success shines its bleary eye on you, there will be a chime tone or display change at the keypad as the switch opens.



If so, congratulations! You’ve freed up the switch. If only light tapping was needed to free it up, the switch was not strongly welded closed, and it has a good chance of being usable (at least in the short term.)



If light tapping doesn’t work, tap progressively harder. The more current and heat generated when the lightning hit, the stronger the weld is likely to be.


Hardwire contacts - Surface-mount


If more aggressive tapping eventually does free up the contact, there was probably a significant amount of current that caused it to weld. This means enough damage may have been done to cause the switch to fail in the near future.




I usually don’t recommend brute force for any switch troubleshooting, due to the risk of possible damage. However, in this case it can’t do any harm.

If the switch is welded enough to require heavy pounding to free it up, it needs to be replaced anyway.



If the weld is very strong, no amount of beating on the switch will free it up. In that case, the switch is hopelessly damaged and should definitely be replaced. For help doing this, see the links at the bottom of this page.


Follow-up to Frozen Switch Troubleshooting


How you proceed after initial switch troubleshooting is something of a judgement call, and will depend on your circumstances. Lightning is never good for any equipment. Even though everything may appear to be working fine, there may be degraded components or hidden damage that won’t surface until weeks or months in the future.

Some important things to consider:


Minor Switch Problems

If there are only one or two frozen switches affected and they free up when lightly tapped, you probably had a lightning strike that wasn’t too close to the house. Test all of the magnetic contacts by opening and closing them several times. If they seem to be working normally, make a note of the problem contacts and leave it inside the alarm panel box. Then go back to using the system as usual.


If you ever have any further switch issues, check your switch troubleshooting notes. If one of the previously welded switches is having a problem again, replace it. It was likely damaged more than it was showing, and shouldn’t be trusted in the long run.




 More Severe Switch Problems


If you have several switches welded shut, or if you had to smack any switches quite hard before they opened, you probably had a fairly close lightning strike. Switches that have undergone this abuse are more likely to fail prematurely. If there was no other damage to the system, you may decide to take your chances, and simply replace any switches that do fail.



If you found welded contacts and also had damage to the main alarm panel or other electronics in the home (computer, television, refrigerator, etc.), you should consider filing a claim under your homeowners’ insurance policy. Depending on your policy terms, it may cover the replacement value of  the damaged items.


Sample letter of Lightning Damage Claim Form

If you file a claim, your insurance company may require that you have an alarm company check your system and complete a letter or form stating that lightning was the cause of the damage.


In my experience, the insurance company may also insist that all of the magnetic contacts, and in fact all of the alarm equipment be replaced.







A word about hardwired versus wireless systems...



This page deals with lightning damage, which I have only seen in hardwired security systems. Wireless systems are relatively immune to this problem, barring a direct lightning strike on the home.

Does this mean you should avoid a hardwired system for fear of possible lightning damage?

Absolutely not. Lightning damage is extremely rare, compared to the relatively common issues you would be likely to experience with a wireless system. These include:

-False tamper alarms due to cracked and brittle transmitter covers -Wireless reception problems due to interference and location -Periodic required battery changes

The Bottom Line?



Always choose a hardwired system if wiring is possible and economically feasible. Hard wiring is, and likely always will be, the most reliable way to connect alarm components.




Do you have a lightning damaged alarm system, or an older system that’s starting to have problems? If so, why not get a few free alarm quotes?

Knowing how much a new system would cost will help you decide whether you should try to fix the old one or just replace it.

These quotes are absolutely free!

There is no obligation to buy, and no credit card information is requested.




Product Links

Surface-mount switches

Recessed switches

Crimp connectors / B-Connectors for replacing switches


Related Articles

Troubleshooting Intermittent or Falsing Zones

Removing Magnetic Door and Window Contacts

Installing Surface-Mount Switches

Installing Recessed Magnetic Switches



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