Alarms are good for

1. Insurance discount, it turns on by itself, self arms, siren and starter kill

2. Door lock operation

3. Flashes parking light

4. Nice LED, they will rob the car next to yours and avoid yours

5. Adds another starter kill that comes on with alarm

6. Adds a impact sensor, FACTORY alarms DO NOT Have this

7. Factory alarms are ALWAYS in the same place. AFTERMARKET alarms are NOT

8. extra remotes

9. Piece of mind

Need more reasons? Its cheap, its good security, get it.