Unless someone has modified - ie replaced the ECU without immobiliser function still active. It has one.
This is basically (not trying to cover everything involved or use different transponders in the key) where the BSI reads the key, compares that it is approved for use, then the code sync is correct/expected, and then unlocks the ECU allowing start of the vehicle. It is also why you post(s) saying, the BSI and ECU are matched pairs or immobiliser purgatory will visit, etc (cloning options/repair of the ECU or replacement of both BSI / ECU together).

The alarm is optional.

Also why a procedure exists to avoid BSI corruption when changing the main battery and why often need to turn to 'on' without starting the engine for 1-3 minutes to allow sync of the key with the BSI after battery change or it won't start.
BSI Reset / Battery Disconnection / Reconnection - French Car Forum

Hope you find this useful.

 

Thank you for your reply, RedSector, very helpful indeed.

I always used to replace my batteries myself on my all cars. Undo and redo two clamp nuts and the nut holding the battery in place, and the jobs a good un. Obviously there was no BSI on them, so just as well you mentioned the necessity to sync the key after battery replacement, or I would have ended up in trouble! Thanks for the link as well.

"It is also why you post(s) saying, the BSI and ECU are matched pairs or immobiliser purgatory will visit, etc (cloning options/repair of the ECU or replacement of both BSI / ECU together)."

Does that mean that the BSI and ECU are inextricably linked and one should not be replaced without the other, or be sure to check whatever one intends doing with one is possible without conflicting with the other?

 

Most sites will answer the question for you, because they know Peugeot’s have a standard factory fitted immobiliser. There is probably a box to tick for this, together with asking if the car has been modified.

 

Thanks for your input, OP.

Yes, you're right, about the question on modifications and these are the options for Alarm/mobiliser.

Factory Fitted Thatcham approved alarm/mobiliser
Factory Fitted Thatcham approved alarm/mobiliser
Factory Fitted Non-Thatcham approved alarm/immobiliser
Factory Fitted

The chances are is that there is still the original ECU fitted however, owing to not knowing the full history and based upon yours and RedSector's reply, it would appear to me that the only way I will know for sure is if I get it hooked up to an OBD. Does that sound right?

 

Check prices between these two, I bet its a couple of quid

Factory Fitted Thatcham approved alarm/mobiliser
Factory Fitted Non-Thatcham approved alarm/immobiliser

I usually go for the second one to be safe

 

Thanks for helping out Gibbo,

"It's a funny old world" as the late legendary footballer Jimmy Greaves would say.

I ran Comparethemarket choosing "None" for the Alarm/immobiliser question on Monday just gone, then today with Factory Fitted Non-Thatcham approved alarm/immobiliser and it brought up the same insurer in the number one spot, 1st Central. You were right about the £2, However, it was £2 MORE expensive when fitted with one than without one?? I then ran it with Factory Fitted Thatcham approved alarm/mobiliser and it came up with the same price. Lastly I ran it, choosing "None" again, and it gave me the same insurer in the number 1 spot, £1.46 more expensive the last run and about £3 more expensive than when I ran it choosing "none" on Monday. I guess from moneysavingexpert site that premiums creep up the nearer one get to the renewal date. They reckon the best time to look to renew is about thirty days before the date.

Anyway, in the absence of not being able to check for sure if there is an immobiliser fitted without hooking it up to an ECU diagnostic machine, I'm just going to choose "None" for the sake of £1.46 extra! I can always try going through the link in the email from Monday and see if I get it another £2 cheaper

 

The immobilser is a Thatcham Approved - Cat 2. So option 1 in the list - Factory Fitted Thatcham approved alarm/mobiliser

It's a TC2 type. Transponder, Contact, 2 circuits.

 

Thank you very much dibs that's great info only trouble is I don't know if the ECU has been changed sometime in the history of the car, see Redsector's first reply above. I thought there would be a significant difference in the insurance premium for a vehicle with an immobiliser and one without. However, it is only about £3, so I think I will take the without option to be on the safe side. I can always confirm this if and when I need to use ECU diagnostic in the future to resolve a fault. Thanks again!

 

Simple test would be to take the key "apart" like you are going to change the battery in the fob, take out the board, close it back up & see if the car will start just with the blade. I'd be surprised if it did.

Modified ecu's removing the immobilizer are unlikely on a 207 in my opinion.