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MG MGF Technical - MGF Car Alarm


Sorry if this goes a bit off topic!

First of all am I correct in thinking that my Y2000 model 1.8i is equipped
with a Thatcham Category 2 Alarm/Imobiliser (i.e. the standard factory one)?

Second of all if this is correct has anyone upgraded to a category 1 system?

The local alarm shop say that the only option I have is to take a 2:1 upgrade. The only problem with this is that I end up with two alarm controls. So every time I want to alarm the car it will be 2 blips for the
standard MG alarm and 1 blip on the other third party alarm? (I can see this being a pain)

It all got confusing but they basically said:
1) that the standard MG one can not be upgraded and a separate control is needed
2) the MG one can not be taken out and replaced by a new "full" system as it links in to the engine management system
3) fitting a "full" system over the top would result in complications with both trying to arm/disarm the car

I know the standard alarm system is pretty good but I wouldn't mind a bit more security for all those well..... "not so nice areas" :-) So, has anyone upgraded their alarm and if so did you manage to keep it down to just 1 alarm control?

Chris Birch

>So, has anyone upgraded their alarm and if so did you manage to keep it down to just 1 alarm control?

No, as you found already yourself. Impossible.
You will end up at last with an additional alarm blipper.

Dieter Koennecke

I have had this problem on several cars, not MG f's though.

It is not a good idea to have to seperate alarls, especially if you intend to use both and your neighbours will problably not like you any more, with alarms that use voltage sensing the di-arming of one will set off the other and as it is difficult to operate two remote controls at the same time for a few seconds you could have an alarm going off.

Does anyone know if the std MG alarm has voltage sensing?

Radar detection can co-exist with ultrasonic, but ultrasonic detection is not a good idea for a soft top and cannot be used with the top down. I know little about the MG alarm, but I think it uses radar to give protection when the hood is down.

I personally reccomend that if you want extra security for your f you go for a stand alone imobiliser in addition to the alarm.

This will cut two circuits and earth them so making "hotwiring" difficult (usually the starter motor solenoid and either the fuel pump or ignition coil).

All good imobilisers are pasive arming, which means the imobiliser will cut the circuits automatically a few seconds after the ignition is switched off. To swicth off the imobiliser you will either need to insert a small jack plug into a socket, present a proximity tag to a sensor or in some cases type in a code number on a key pad. The imobiliser is then off for a few seconds until the ignition is switched on and will remain off until the ignition is switched off.

Personally I would go for physical security if youi think there is a threat to your f whereby the standard system will be inadequate, eg wheel clamp, steering lock,garage etc.

Any one know the difference between Thatcham Cat 1 and Cat 2? I'm not too sure, I thought one was an alarm and the other an imobiliser, but I'm not certain

class 1 has separate battery backup,so still works if cable cut or disconnected. May also need other to qualify.

"class 1 has separate battery backup, so still works if cable cut or disconnected. May also need other to qualify."

Not quite correct actually, but to be a class one it does have to have battery backup I believe.

Class one is alarm & immobiliser together. Not sure what criteria these have to reach though. So the Rover unit has a Thatcham approval for the immobiliser but not for the alarm, making it class two.

Class two is the immobiliser stand alone (no alarm required). Therefore there is no class one system for immobiliser only. (Missus has one on her Clio).



I'm sorry for the question, but would upgrading to Class 1 System by use of aftermarket parts result in decreased insurance costs in the UK ?
Or do you intend to improve the security only cause of your own individual interest ?

Dieter Koennecke

class 1 must have sepearate siren with intelligent battery back up,also must have single colour security
wiring loom plus to gain insurance approval be fitted by registered fitting company.A certificate of test has also to be filled in with car details and alarm type if not fitted as OE. Some insurance companies like class 1 on certain cars some will now only insure fully if fitted with class 1.

I may be wrong but I understood that to be Class One you also had to have a fixed 'tin-top'.

Ted Newman

No Ted one of my other cars is a VW Golf GTI Cabrio this has a class 1 sigma alarm. For the full spec on the differences Thatham have their own web site.Recently checking on prices for insurance some companies were quoting group 17 and must have class 1. My renewal from my existing insurance was better and i did not change.

>>Does anyone know if the std MG alarm has voltage sensing?<<

Yes, I believe so. IIRC, this is how the perimetric alarm function works- by detecting the voltage drop associated with switching/activation of interior lights...

Thatcham I alarms, in addition to the criteria mentioned above, also requires passive alarm activation. In an MGF, the plipper must be used to activate the alarm, although the imobiliser kicks in passively and automatically- hence the class II rating.
Rob Bell

The alarm certainly goes off if you open the "front" boot without disabling the it first (even if you have the "rear" boot open at the time to get to the catch!)...

As there's only one switch under there (that controls the light) I can only assume voltage sensing is at work...


Don't waste your money upgrading - a thief will get round any alarm or immobiliser in seconds or at the most a minute or so if they know what they're doing. It's just the speed it happens that's affected.

It's a game of making your car less attractive to steal compared to the others on the street - a much better way is to use physical security like Disklok (big yellow metal steering wheel lock) that cover the whole steering wheel. They are easy to put on and off but would cause a thief a lot of aggravation to remove and they're highly visible. I've been using one for a long time and wouldn't dream of leaving my car over night without - despite the alarm immobiliser.

The cars with the better security systems incorporate physical security such as deadlocks too - MGF has this (always superlock your car if you can) plus visible VIN numbers and window etching.

at this present moment my mgf is stuck in superlock mode ican open the drivers door with my key but passengers door remains locked can anyone help please

Agree with James except that a decent Thatcham class one system will probably thwart (sp?) the oppotunist thief..A pro will get the car whatever system you have installed. It's all about getting the theif to think twice about your car & move onto something easier i.e. not alarmed....


The reason behind upgrading was two fold. Firstly a little more peace of mind and secondly the price of a usual 2:1 upgrade would be made back in three years of ownership through a reduced insurance premium (for me anyway).

I already use the big yellow disk lock and agree its excellent albeit masive, a nightmare and a bit to big for the boot.

I was just baffled that MG would fit a Cat 2 alarm that wasnt upgradable. After all it is a desirable sports car.

I know people today only give the minimum that they need to to meet standards etc but many young drivers or drivers with only a couple of years no claims need a 2:1 upgrade to get insurance.
Chris Birch

Hi Chris have you also fitted a class 1 alarm alongside the MG OE one. Is the MG alarm not suitable to upgrade because of cost or would it need to be totally rewired to self colour cable? are you now using both alarms or have they disconnected the MG one.I have just bought a new MGF and think its poor its not fitted with a class 1 alarm as OE.


my 2 pence worth

The standard F alarm/imobiliser is in my opinion
pretty good and effective, to me the alarm part
is not important anyway - ask yourself who cares
nowadays if you hear a car alarm going off
The imob. is passive arming which is good

Car comes with deadlocks again pretty good
MG could of gone to town on a wizzy alarm but then
it would of cost extra to you, and less sales to MG

If your personally worried then fit an extra alram,
you have nothing to lose, and gain peace of mind
Im not sure an MGF would be desirable to organised
car thieves?? I wouldn't of thought the market and
margins were there

I agree that the best things to save your car
is something visable like the steering lock
the car thieves your going to come accross are the
local teenage yobs who want a cheap ride home
after kicking out time

Certainly round the villages here in Berks/Bucks
car crime is rife, but with all the flash cars here
they are not the ones being nicked and burnt out it's
your nova swings and your fiesta populars because they
are pre car makers having alarms as standard

The trouble we do have is organised thieving *from*
cars, there is a gang working this area at the mo and
following people from where i work in daylight to
steal laptop, moblie phone, PDA etc. as soon as the car



I use the COMUSAT alarm system which is a satellite based system. In case of troubles, it calls my cellphone, i can stop the car at distance, locate it and call the police.

Very efficient and never caused any electric problems with my F.

the website of this system is : (french)
I dont know if it is available in Great Britain.


This thread was discussed between 06/05/2001 and 10/05/2001

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