Key sets off alarm

Battery on key fob failed today so had to use key to unlock drivers door. This immediately set off alarm.

From researching here and on other forums, varying answers to this. Does anyone have difinitive answer ?  As seems something wrong. Also happens on passenger side but not on boot. Putting key in ignition doesn’t stop immediately - takes a while. New battery in key fob stops alarm.

Is there a way to stop alarm with key ? 

Any help please


Starting the engine will silence the alarm.

Thanks. Should this happen straight away ?  Can start engine no problem but alarm continues then stops then hazards on for a while then alarm  back on. Can’t play around with it too much because of neighbours 


Sounds like it’s not the factory alarm then. What shape are the buttons on the transmitter?

By transmitter you mean fob ?

There are 3 buttons - lock, unlock and boot. I would say look like a tunnel shape or underlined n


Does it look like this…

This is the only Mazda fob available, marked Visteon 41703 on the back. Anything else will be aftermarket - highly unlikely on a MK2.5 car. 

Yes exactly like that. Fob works fine. 

Looks like a trip to auto electrics for me then. Thought it might be something simple that am not doing. 

Tried locking and unlocking with key. Tried holding in unlock position for few seconds. Does it on both doors - so I guess unlikely to be switch on door lock…


is the fob locking/unlocking the doors OK?

There really isn’t much to this system and if the fob is working the only other thing I can suggest that would cause a problem are the central locking micro switches that operate both door locks. I have recently seen these, particularly the drivers side giving more problems on the MK2.5.  


starting the engine should turn off the alarm. The door key cylinder switches do give trouble, they get water in them and stop working. Maybe both of yours have failed but the boot one is still OK, hence opening the boot with the key turns off the alarm but the doors don’t.

Thanks guys.

Yes fob works fine now with new battery. 

I did read somewhere that it is a feature of the car that when opened with key that alarm will go off and can surprise new owners - which it did with me. 

What is worrying is that starting engine doesn’t turn off alarm. Would this happen if switches were faulty ?  2 out of 3 times yesterday locking and unlocking passenger door with key alarm didn’t go off. Will try again today - don’t want to upset neighbours too much !

Will also try setting alarm off with key and seeing if using lock in boot stops it

Cheers Pete

Thinking about it, I may be thinking of the NC that turns off the alarm when the engine is started, sorry.

Thanks Robbie.

No doesn’t work on mine - starting car makes alarm go faster !

Here’s what I have discovered today. If I lock drivers door with fob or with key and unlock with key, alarm will go off - this can be silenced by opening boot with key - shut boot all OK. This is a bit of a faff but at least I know what to do next time battery in fob goes or fob breaks.

If passenger side is locked with key - opening with key does not cause alarm to go off. However if door is locked with fob and opened with key alarm will go off and can only be silenced by using fob or opening boot as before.

My question now is. Is this standard or does it still point to faulty switches on lock barrels ?