Let's talk car alarms.
First off, disclosure. Between mid 1986 & mid 1989 I worked as an electronic design & development engineer for EDA Sparkrite in Walsall. Who, for those who don't know, made car alarms for the afterfit market.
The first thing I want to say isn't of earth shattering importance, but cars & their components are made to provide the maximum profit for the minimum cost. Just because the car costs x thousand
pounds to buy, it shouldn't be assumed that the car alarm that's fitted would cost a comparable amount or contains sophisticated electronics. Usually it's dirt cheap electronics & can be
purchased under it's trade name cheaper. I have personal knowledge of this.
At the start of the comments it was said that if you can remove the hood, & access the battery & fuse box then a mistake has been made. With the afterfit market, there were usually plunger switches provided, (like those used to turn on the interior light when the door is opened), to protect both the boot & the bonnet. So if these have been omitted, it's most lilely for cost.
Saying that, it's not hard to disable a car alarm. The first way is to take a core of either 2.5mm or 4mm twin & earth cable, & attach a croc clip to either end. Attach one end to the connection to the horn, the other to the body work, & then trigger the car alarm, & if the manufacturers have skimped on the number of fuses, pow, the fuse blows & with a 'bit of luck' disables the car alarm. the second way is similar to the first but involves smashing the headlight & earthing the headlight bulb's filiment with similar results. The handbrake is on? Then a pair of strong wire/bolt cutters applied to the handbrake cable solves that problem.
Of course, if the aim is ti merely steal from cars, then a classic attack method is to constantly trigger he car alarm at night, then with some 'luck'. the cars owner will disable the alarm & then the car can be broke into at leasure. A 'personal' story is one that happened to my ex-brother in law & his friend. They decided to go rallying, & to this end took a ford escort & made it into a rally car. This was easy for them to do as both were mechanics & the friend had his own garage. They built the car & used it, when one morning six months later, the car was found to be missing from the friend's drive. Dispite having a Sparkrite alarm fitted. Asking around the nieghbours if anyone had seen anything, one guy admitted seeing the car being pushed onto a low-loader at three in the morning, his excuse for not phoning the police, was that he thought it was being taken away for some work to be done on it!
There is one last method of breaking into cars, simply if a spare fob is ordered, then get an accomplice in the garage to order two instead of one.
This leads to the last problem with car alarms, human apathy. I mean how many people have heard a car alarm going off & paid no attention to it?