Know your GTi: Electronic immobilizer.

While for some vehicles, you need to install an additional immobilizer to prevent break-ins and thefts, the Golf GTi mk5 comes with a built-in electronic one. There is a chip in the ignition key which automatically deactivates the immobilizer when inserted into the ignition lock. Vice versa, when removed, it is activated automatically.

Therefore the engine can only be started using a genuine VW key with the correct code. Any unauthorized keys used, the display in the combi-instrument will show 'SAFE' or 'Immobilizer active!'. And the vehicle can then not be used.

So, don't worry so much about thefts. I think what you should worry more is just vandalism. There are a lot of blind cows whose vehicle does not have a 'stopper' and will slam straight into yours when parked next to your car. Or the usual, smashing of windows for burglary. My advise is, park where vehicles are supposed to be parked. And park somewhere bright. And make friends with the security guard so that he keeps an eye out for you ;)