I find car alarms really irritating, at least the ones that make loud noises to alert everyone that someone wandered by the car a little too closely. Mind you I can live with those, but the ones that really get my goat are those that are so sensitive that they go off almost continuously.
There is one car with a particularly sensitive alarm near my flat that is always going off. One night it was going off every 10 minutes, all night!. The owner obviously needs a lesson in social responsibility.