Gavin Green gets locked in, immobilised and deafened by anti-theft devices
Immobilisers and flash new alarms, I'm told, are the main reason why fewer expensive cars go joy-riding these days. Maybe. But for every thief that an alarm or immobiliser deters, I bet it inconveniences at least 100 owners, and many more innocent neighbours.

In the last three months, I've been stranded in front of a level crossing when the immobiliser decided to immobilise just as I wanted mobility; I've had an alarm squawk dementedly while I sat by looking as innocent and as much like the owner of the car as possible (nobody took any notice: they never do when car alarms go off); and I've been locked out of my car by an over-eager alarm, with the keys inside.

To make matters worse - or at least, more embarrassing - these faults occurred in the three priciest cars I've had on test recently. I was immobilised in a pounds 215,000 Bentley Azure; squawked at by a new pounds 35,000 Mercedes E-class as I stood impotently nearby; and was locked out of a pounds 47,000 Jaguar XJR. Of course, these cars all feature the latest and the most hi-tech alarm/immobilisers on the market. That's the problem. On the other hand my wife's four-year- old Renault Clio 1.2 RL, which has neither alarm nor immobiliser (the car is locked by the old fashioned method of inserting key in lock, which I've always thought quite efficient) has given us faultless, squawk-free service. There's a lesson there somewhere.

The Bentley's immobiliser is terribly flash. Among its features is one which automatically prevents the engine being restarted within 30 seconds- or-so of it being switched off. What's the point? I'm still not sure, but I think it has something to do with preventing crooks from making off with your Azure while you're paying the cashier at the petrol station (something you do rather a lot of in a 15mpg Bentley) should you have left the keys in the ignition. When the would-be thief jumps in and turns the key, nothing happens.

Fine, in theory. But I was held in traffic in my corner of south-west London at a level crossing. To avoid asphyxiating locals, I switched off the engine. When I tried to switch the engine on again...nothing. By fiddling with the buttons on the remote control switch dangling from the end of the key, I managed first to switch on the alarm (lots of noise), then to immobilise the car again (lots of nothing), then to lock the doors with me inside, and finally to reactivate the ignition, allowing me to restart the engine. By this stage the many people behind me who, when I was mobile in my ostentatious Bentley, thought I was a prat, now thought I was a fool as well. To make matters worse, my inactive car was probably worth more than their 20 cars collectively. The bloke behind me was driving an X-reg Escort, probably worth about pounds 500. I suspect he will never again derive so much pleasure from using his horn.

The Mercedes' alarm/immobiliser was almost as perplexing. After unlocking the car with the remote control, (unlock doors, deactivate alarm) you'd have to wait a good two or three seconds before actually opening a door - otherwise the alarm would screech. As with the Bentley, if you unlocked the car and waited a minute or so before starting the engine, you couldn't - for the wretched immobiliser had done its dirty deed. So you'd have to fiddle with the remote control buttons and eventually you'd crack the right combination and your three-pointed star would finally get mobile again. Aaaaarrh!

The Jaguar XJR's system is much simpler, and better, if for no other reason than you can turn the engine on and off without having to fiddle with buttons. Trouble is, for some reason the remote control stopped working for me. I rang a Jaguar dealer who said, no problem, just use the key. It has a "transponder" which verifies that it indeed is the correct key for that car, and will deactivate the alarm and the immobiliser. So I dispensed with the remote control.

Later, I opened the car with the key, shut the driver's door and tried opening the rear door to put my briefcase and coat on the back seat. The car had locked itself (with the keys in the ignition) when I shut the driver's door. Once again, the trusty Clio saw service, until I got hold of a set of spare keys.

Familiarity with these wretched alarms and immobilisers may breed more content. Indeed Doug Wallace from Mercedes assures me that owners quickly get the hang of the things. "Our system is complicated and needs some familiarity. But an owner would quickly master it. We feel we have to do our most to protect our cars. That's why we fit the most sophisticated alarm/immobiliser system available."

Alun Parry from BMW adds: "We fit immobilisers and alarms for the peace of mind of the owner, frequently because insurance companies demand them and sometimes offer discounts on premiums, and to deter thieves." BMW, to be fair, offers one of the simpler engine immobilisers - as long as the correct key is in the ignition, the car can be started. Mind you, the car in my road whose alarm cries wolf most often at night is an L- reg. BMW 320i.

I suppose if I owned a flash car worth a fortune I probably would specify an alarm and immobiliser. The prospect of my car being nicked would demand it (and so probably would my insurance company). But I'd make sure that a nice uncomplicated little car, like my wife's Clio, was on standby for when things went wrong.

The alarm's blaring. Is anyone interested?

What happens when an alarm goes off in an unattended car? Concern from passers-by, perhaps; irritated complaints to the police if the noise persists? Last week I set out to test reactions. I chose three built- up locations, activated the siren, and retired to a safe distance to see if it proved to be an irritant, deterrent or anti-theft device.

First stop was the car park at a major regional hospital. My B-registered VW Golf did its siren stuff, and I retired behind a bus shelter. An elderly couple parking their Honda gave the car a quick glance. It fascinated a toddler being unloaded from a nearby Austin Metro. Other parkers clearly wanted to find a spot as far away from my attention-grabbing Golf as possible. There was no sign of the security company who were supposed to tour the area. No one seemed to make any attempt to report my wailing car. I gave up before frost bite set in. If I detected any discernible pattern of behaviour it was that the over-40s and senior citizens would at least look in the general direction of the noise, while young adults were utterly indifferent.

At lunchtime I found myself outside an East London Chinese restaurant. Parking on the pavement, I set the siren and popped inside for some food. After half an hour the Golf was still screaming, but it had provoked no noticeable interest from passers-by. The owner of the restaurant, however, started to look peevish, so I switched off the alarm.

I moved on to a nearby residential street. It was tightly parked and had Neighbourhood Watch stickers in the windows of most of the houses. This time I decided to stay in the car, posing as a potential car thief. I switched on the alarm and waited to see if I would be surrounded by squad cars and hear a shout of "Freeze!". This was not New York, however - it was Mind Your Own Business suburbia. I think I spotted a few twitched curtains, but that was all.

Finally, after a hard day disturbing the peace in built-up areas, I triggered the alarm in my tiny hamlet: population three plus a flock of sheep. The sheep took flight, of course, but within a minute a neighbour emerged to investigate where the racket was coming from. At least I had succeeded in provoking one member of the otherwise indifferent British public into action.

James Ruppert