One of North America’s most popular SUVs is the Subaru Forester, packed with practicality and massive outdoorsy vibes.
As with any vehicle, the Subaru Forester’s alarm may go off randomly and for unknown reasons.
If your Forester alarm keeps going off, this article is here to help.
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Why Does My Subaru Forester Alarm Keep Going Off?
The Subaru Forester’s alarm can be triggered due to unlocking the car manually with the key, a dying 12V battery, a faulty key fob, accidentally pressing the alarm button on the fob, a faulty hood switch and faulty sensors.
1. Unlocking the Car Manually With the Key (Not Using the Fob)
If you have unlocked your Forester manually using the key then this will trigger the alarm as the vehicle is designed to be unlocked with the key fob. If you have lost your fob, it is damaged or run out of battery, you can silence the alarm with 3 on/off cycles of the ignition key.
If you use your fob for lock/unlock this will not set the alarm off.
Here is what owners on subaruforester.org had to say:
“If you locked it using your remote, it enables your alarm. Unlocking it using the key manually will trigger the alarm and pressing your unlock key on your remote will disable the alarm. So you have to use your remote to unlock whenever you lock it using your remote.”
“Your security system is working normally, as the key lock doesn’t deactivate the armed security system. If you want to use your key to unlock the door, without having the alarm go off, you need to lock your Forester without arming the security system.”
“You can also stop the alarm by turning the key on and off in the ignition a few times. I never remember how many times it takes; three I think. I just keep at it till the horn stops blowing. This is handy if you’re using a spare key with no remote.”
2. Dying or Weak 12V Battery
If the 12V battery is dying or has an insufficient voltage, it can trigger the Forester’s alarm.
This is a leading cause of intermittent false alarms and mysterious nuisance alarms.
A 12V battery usually last 3 – 5 years before needing to be replaced.
Before swapping the battery, inspecting the one under your Forester’s hood is worthwhile.
A loose or faulty connection can also cause the battery not to work correctly.
If you have a multimeter, check the battery yourself. If not, head to your nearest AutoZone – they offer free battery health checks.
You can also try disconnecting the battery, cleaning the battery’s terminals, and then reconnect the battery. When reconnecting the battery, make sure the connections are tight and free of any obstructions on the terminals.
You can clean the terminals of your 12V battery using a toothbrush dipped in baking soda and water mixture.
One owner on the scoobynet.com forum posted how they diagnosed and solved their alarm going off:
“Car battery for me as well. I hadn’t used the car for a while, then woke up at half 2 in the morning with the alarm going off. had to go into my garage, get a spanner and disconnect the battery. Charged it the next day and all has been fine since! (Car back on the road).”
3. Faulty Key Fob
A key fob that is dirty, damaged, faulty, or needs a replacement battery can trigger your Forester’s alarm to go off randomly.
Open your key fob (as if to replace the battery) and clean any dirt, grime, and grit that may have entered the device.
Clean the battery contacts carefully with some rubbing alcohol and a soft cloth.
If you close the key fob and the alarm is still triggered, you should change its battery.
These key fob batteries are cheap to buy and will save you a lot of sleep and worries.
Once you’ve replaced the battery, try to lock and unlock your car using the key fob. If the alarm still goes off, you may need to contact your dealer or an auto-electrician.
One user on the subaruforester.org forum shared their experience:
“It turned out to be a bad key FOB, even brought the car to the dealer and when I left it stopped, when I came back it started again. I had the bad FOB in my pocket to replace the dying battery in it…dying because it was stuck in panic mode forever.”
Related: Subaru Forester Beeping? (12 Causes & Solutions)
4. Accidental Press of The Alarm Button On The Fob
A common yet often overlooked reason why a Forester alarm goes off at random is due to owners accidentally pressing the alarm button on their key fob.
Here’s what owners on subaruforester.org had to say:
“I had this problem on my 07 as well, turns out the button was getting pressed in my pocket when I would sit down.”
“That’s it for me……nearly once a month. The poor neighbors when I’m, out late until 2:00 AM !”
5. Hood Latch Sensor Problems
The Forester, like most vehicles, has a hood switch. It is designed to trigger an alarm if someone tries to force open the hood – if it is broken or dirty it can cause the alarm to go off.
Dirty / Rusted Hood Switch
Due to the location of the hood switch, its not uncommon for it to get very dirty – this alone is enough to trigger the alarm at random. Corrosion and rusting of the hood switch is also very common, which can also trigger the alarm.
Its a good idea to give the hood latch a thorough clean to remove any gunk buildup.
It’s also a good idea to spray a little WD40 too lubrication.
Faulty Hood Switch
It’s not uncommon for the hood switch to get damaged or fail completely.
If the switch that monitors whether the hood is open or shut isn’t working then this can trigger the alarm.
Replacing the hood switch is a fairly cheap and easy process, however if you are not mechanically inclined, have your local dealer replace it for you.
Here’s what a UK owner had to say on subaruforester.org
“I went through the usual things and checked all door switches as before, then checked the bonnet [hood] switch and hey bingo that was the culprit.”
6. Faulty Door Switches
A faulty door switch is another common cause of a Forester alarm going off.
Similar to the hood latch sensor, your Forester’s alarm monitors the doors to make sure no one is opening them when they shouldn’t be.
It’s a good idea to give all door latches a clean and some lubrication with WD-40, open and close the doors to work it in.
Door switches can fail or become damage due to general wear and tear.
Your Subaru dealership should be able to run diagnostic tests to pinpoint which door switch is faulty and triggering the alarm.
Alternative Suggestions
Disconnect the Battery
Sometimes mysterious alarm problems can disappear with a simple reboot, there are no guarantees here but it’s worth a try.
Disconnect the battery for 20 seconds and this resets many of the electronics in the vehicle.
Pull the Horn Fuse
On some Subaru Forester models by pulling the horn fuse you disable the alarm temporarily until you find a solution.
Check For Warning Messages
When the alarm occurs can you see any lights or warning messages on the instrument panel?
This can give a clue as to what’s causing the alarm e.g. ‘Hood Ajar’.
Take it to a Subaru Dealership
If needed, take your Subaru to the dealership.
Tell them you are NOT paying for a check on what the problem might be.
Ask them if they will check it for free.
Most dealerships and other places do quick/initial diagnosis for no money as they plan to make money for the repair of your vehicle.
If you’re Chevrolet is still under warranty then they should fix and resolve the issue for free.
Check for Recalls or TSBs:
By entering your car’s VIN number on Subaru’s recall page or the NTHSA’s Safety Issues & Recalls page you can determine whether or not there is a TSB or recall for your vehicle and if there is you’ll want to get it addressed.
A recall is issued by a vehicle manufacturer for issues that are safety-related, while a TSB covers components that may be malfunctioning but don’t compromise the safety of the vehicle.
Test the 12V Battery
How to Test the Battery
- Before testing, remove the surface charge from the battery, this allows for an accurate reading.
- Simply turn on the headlights for 2 minutes then turn off.
- Set the multimeter dial to the ’20 Volts’ setting.
- Make sure the car is turned OFF
The multimeter will have a red probe and a black probe:
- The red probe is for making contact with the positive terminal
- The black probe is for making contact with the negative terminal.
Measure across the battery terminals.
- The meter should display a reading, if the battery is fully charged the voltage should be between 12.2 and 12.6 volts.
- Anything under 12V and the battery should be charged or replaced.
Related: Subaru Forester Headlights Burning Out? (11 Common Causes)
Resources
https://cdn.subarunet.com/stis/doc/ownerManual/MSA5M2102A_STIS_opt.pdf
https://cdn.subarunet.com/stis/doc/ownerManual/4491805-2021_FORESTER_GSG_2nd.pdf
