I don’t know about other after-market car alarms, but the sensitivity of the Viper 5901 I recently purchased is adjustable. When I first brought the car home after installation, it seemed like every other passing car would activate the warn away alert or initiate the full alarm.
Guess what?
I took it back to the store and had the installer adjust the sensitivity.
How hard is that? I hear nary a peep out of it now except when someone lingers around the car, which initiates soft rapid chirping sounds to “warn away” loiterers or potential thieves…exactly what I want it to do. (If they don’t move in a timely manner, the full alert is triggered.)
Just for the record, some newer after-market alarms have built in timers that restrict how long it stays on. Mine defaults at 30 seconds, with the option to change it to 60 seconds, so it’ll never continually stay on.
And to @Knotmyday, I don’t know if auto alarms have the ability to call someone’s cell phone, but some models do send a signal to the car owner’s key fob/remote control that mimics the car’s alarm. In other words, if my alarm goes off now, my remote control will vibrate and produce an audio alert. This allows me to immediately respond to the situation (visually inspect, cancel alarm, call police, etc.), so there’s no valid reason for anyone to say my alarm is a nuisance.