JW,

The factory alarm will only sound when the doors, hood, or trunk is open. It
won't sound the alarm if the glass is smashed, nor will it sound the alarm, if the car thief comes with a tow truck, UNLESS you get the optional glass-breakage sensor and the other sensor ( damn, forgot the name ) that will sound the alarm if someone tried to tow away your Volvo. For now, my factory alarm will do, but down the road when it will have to be parked outside to make room
for my new car, then I will get the glass-breakage sensor and the other sensor.
Both sensors will run you roughly $ 300-$400 Cdn installed, as quoted by my
Volvo dealership.

Hope this helps !

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Kenny
2001 Nissan Pathfinder SE
1998 Volvo S70 GLE