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.”
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 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.
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.
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.)
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.
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.
Also, over time we can lose track of exactly which zones connect to what. Heck, I installed my entire system myself, but I wouldn’t know every zone location without a zone list!
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.
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:
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.
Begin 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.
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.
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.
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.
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.
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.
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 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.
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 may 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.
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 alarm equipment be replaced.
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!