The Subaru BRZ is a two-seater, rear-wheel drive sports car beloved by driving enthusiasts the world over.
Having said that, the BRZ’s alarm can be triggered by random and unknown causes.
The BRZ shares near identical underpinnings to the Toyota 86, so we’ve researched forums for both models to find the most common causes of the alarm going off.
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Why Does My Subaru BRZ Alarm Keep Going Off?
The Subaru BRZ’s alarm can be triggered by oversensitive or faulty door alarm sensors, a dying or weak 12V battery, a faulty hood switch, accidental press of the panic alarm, a weak or dead key fob battery, or unlocking the car manually with the key (not using the fob).
1. Oversensitive or Faulty Door Alarm Sensors
The Subaru BRZ alarm can be triggered randomly – and oversensitive or faulty door alarm sensors are one of the most common causes.
These vehicles are equipped with a robust alarm system.
As many owners have found out, the alarm systems are incredibly sensitive straight from the factory and dealership when new.
The BRZ’s alarm system has a sensitivity setting that can be adjusted.
The default setting of the BRZ’s alarm system is set to its maximum. This can be adjusted by a dealership or workshop upon request.
Faulty door alarm sensors will trigger the alarm at random times, too. Any deviation of the alarm’s sensor position or misalignment can sound false alarms.
To diagnose the root cause takes a bit of detective work.
An owner on the FT86 Club forum shared their experience of the oversensitive or faulty door alarm sensor problem:
“After ten minutes, the alarm actually activates as if someone were breaking into the car. It’s happened six times in five days, the first occuring right after I got the car home from the initial purchase at around midnight. I felt like a total ass. The neighbors were probably like, “Damn dumbass…showing off and his new car…””
“I called the dealership yesterday and it looks like a faulty (or misaligned) sensor in the driver’s side door. I’ve got an appointment this afternoon to have it fixed.
This is how the service dept guy told me to diagnose it:
1. Start the car and then turn it off approximately 30 seconds later.
2. Exit the car and lock the doors with the key FOB.
3. Wait for the alarm to arm itself. He said to wait 1-2 minutes, but I had to go do something so I ended up waiting about fifteen minutes.
4. Tug firmly on the driver’s side and passenger’s side door handles. Also pull up on the trunk.
5. If the alarm sounds, then make a note of which opening caused it, and bring the info to your dealer to have that sensor adjusted/replaced.
I yanked on the passenger side and trunk and nothing happened. I barely touched the driver’s door and the alarm sounded.”
The same owner updated that forum thread with insight on the solution:
“Just got the car back from the dealer and my issue has been resolved. Apparently the door/trunk sensor’s have an adjustable sensitivity. The service lady stated that the driver’s side door was set at its highest sensitivity, which is 8. They turned it down to 2.”
2. Dying or Weak 12V Battery
If your BRZ’s 12V battery is dying or has an insufficient voltage, it can trigger random and mysterious false alarms.
It is a leading cause of intermittent false alarms and mysterious nuisance alarms.
A 12V battery usually last 3 – 5 years in a BRZ before needing to be replaced.
Before swapping the battery, it is worthwhile inspecting the one under your BRZ’s hood first.
A loose or faulty connection can also cause the battery not to work correctly.
If you have a multimeter at home, 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 reconnecting the battery.
When reconnecting the battery, ensure 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.
3. Faulty Hood Switch
The BRZ, like most vehicles, has a hood alarm switch. It is designed to trigger an alarm if someone tries to force open your BRZ’s hood – if it is broken or dirty, it can also cause the alarm to go off.
Faulty Hood Switch
It’s very common for the BRZ hood switch to get damaged and bent out of place.
If the switch that monitors whether the hood is open or shut is faulty, then this can trigger the alarm.
Here’s what UK owners had to say on the forum GT86OwnersClub:
“Try looking to see if the bonnet [hood] sensor has been bent, mine did the same so I just bent it back into position and no more alarm!”
“It was the bonnet [hood] sensor!! People aren’t kidding when they say it’s flimsy! Thanks for the reply.”
“The [hood] sensor is on a stupidly thin bit of metal, I had this causing my alarm to go off randomly. Simply bending it back ever so slightly was enough to fix the problem for me.”
Dirty / Rusted Hood Switch
Due to the location of the hood switch, it is not uncommon for it to get very dirty – this alone is enough to trigger the alarm randomly.
Corrosion and rust on the hood switch are also common, which can also trigger the alarm.
It’s a good idea to thoroughly clean the hood latch to remove any grit and grime buildup.
It’s also a good idea to spray a little WD40 to lubricate the hood switch.
4. Unlocking the Car Manually with the Key (No Using the Fob)
If you have unlocked your BRZ using the key, then this will trigger the alarm, as your BRZ is designed to be unlocked with the key fob.
When you open the door, the alarm will be triggered.
Here’s what one GT86 owner had to say:
“Used the manual key to get in and, of course now the alarms going off!”
To disarm the alarm, you will need to insert the key into the ignition and turn to the ‘ON’ position.
It will deactivate the immobilizer and disarm the alarm.
5. Key Fob Issues: Low Battery, Dirty or Faulty
A key fob that is dirty, damaged, faulty, or has a weak battery can trigger your BRZ’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 cotton swab.
If you close the key fob and the alarm is still triggered, you should change its battery (it’s worth getting a good quality one).
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 GT86 owner shared their experience :
“I had exactly the same problem around 6 weeks ago. I just dropped the car off at my local dealer to run some tests. Turned out that both fobs died on the same day. Replacement battery in both and away we went.”
6. Activate the Alarm on your New-Generation BRZ
Interestingly, a quirk of the new-generation BRZs delivered to owners in the US is that their alarm systems are not activated. This requires owners to activate the alarm. When doing this incorrectly, random false alarms can occur.
Here is what one owner shared on the GR86.org forum:
“I recently purchased my 2023 GR86 Premium and was surprised to find out that the alarm system came disabled from the factory.
You can test it by lowering the window, lock and arm the alarm, keep the key fob away from the vehicle, wait 30 secs, reach in and flip the lock lever, and open the car door. This should trigger the factory car alarm. If it doesn’t sound the alarm, that means the alarm is deactivated.
Despite what the manual says, you can activate the factory alarm by putting the car in accessory mode, lock the door, then unlock the door, open the driver’s door while pressing and holding on the door unlock switch and continue to press for approximately 15 seconds after the driver’s door has opened. The car honks once when it’s activated and twice if it’s deactivated.
You can repeat the testing procedures by lowering the window, lock and arm the alarm, keep the key fob away from the vehicle, wait 30 secs, reach in and flip the lock lever, and open the car door. This should trigger the factory car alarm.
The owners manual says to press the lock but for me it worked using the procedures above.
When the alarm goes off, you should get a notification from the Toyota app as well! Hopefully it works for you!”
7. Accidental Press of The Panic Alarm Button On The Fob
A common yet often overlooked reason, why a BRZ alarm goes off at random, is due to owners accidentally pressing the panic alarm button on their key fob.
This can be easily done if you’re wearing tight pants and you bend down to pick something up.
The panic alarm button is the fourth and final button on the key fob on new BRZ models.
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.
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.