Most insurance companies offer discounts for the following anti-theft devices:
Alarm Only. An alarm system that can be heard at least 300 feet away for at least three minutes.
Active Disabling. An alarm system that includes a manually activated turn-off feature that disconnects the ignition or battery should someone try to steal your car.
Passive Disabling. An alarm that automatically engages a device which disables the ignition, battery or other vehicle feature that a thief would need in order to steal your car.
Even though some devices, such as a steering wheel lock, do not provide a premium discount, it is still useful to have one in order to safeguard your car from theft.