You can't keep a determined burglar out. Think car jack, sideways, in a door frame. They're in.

You can make it tougher to get in. Have an alarm system and use the darn thing.

I find the best method is - neighbors. Encourage them to call if anything looks wrong. Emphasize you will do the same. Is that car not "right" - call the cops. People wandering the neighborhood - call the cops.