Happy New Year all,
Due to the limited window of opportunity with swapping out dying remote batteries before the fobs lose sync I now use an RTL USB TV dongle with SDR software (usb sticks are about £6-10 from fleabay or similar. SDR console is free or GQRX in Linux). A very cheap spectrum analyser.

In a nutshell set the receiver frequency to 433 mHz and then press and hold key fob. You should see a big spike appear on the display that coincides with your button press. I have done the remove alarm antenna mod so dropping range isn't a useful combat indicator!
The smaller the spike, the lower the battery charge. Change if required.
Cheers
Hoppy

That's interesting - and useful as a second check for any of us with remote alarm/locking

Thanks

Same setup can be useful for checking remote interference. At my house I saw 433Mhz peaks appearing every 20-30seconds (but six months after I bought the car). These were flattening my battery overnight until I disconnected the mk2 receiver antenna.

One day I will buy the updated receiver, but for now I just use the fob next to the rear window.

Good to know!

As a note for changing batteries.. I tell owners to change the batteried with the vehicle UNLOCKED (or at least locked with the key in the door, rather than remote - but unlocked is better!) - as if it is unlocked and alarm isn't armed, then it is just a case of resyncing the fob in the ignition (where passive immobilisation/'friendly sync' is enabled) or in the drivers door.

If the vehicle is locked with the remote and then it loses sync, then unlocking with the key in the door will only open the drivers door, and the vehicle will expect the EKA. I have heard of some owners having luck (again where passive immobilisation/'friendly sync' is enabled) just putting the key in the ignition and it sorting itself out, but then there are also the nightmare stories of being locked out, immobilised in a parking lot, and finding it won't accept the EKA because of a faulty drivers door latch microswitch... usually in the middle of the night, in the p*ssing rain.. all because the vehicle was locked with the remote, and then the batteries were changed and the remote subsequently lost sync.

With the vehicle unlocked or locked with the key (as it will then let you unlock with the key and start it again) you avoid the issues if the remote loses sync, and it can just be resynced and away you go.

I couldn't of explained that any better. Spot on.

Don't do anything to these vehicles while in a locked state.