A security system doesn't have to have all the bells and whistles to frighten away thieves. It doesn't even have to have teeth. Well-placed thorny bushes, landscape lighting, or even a streetlight can double as a guardian.
Start burglar-proofing when you're planting. Trees make great shade, but can also lead burglars to upper stories where you are more apt to leave windows open or unlocked. Plant trees far enough away from the house so that they don't provide easy access to the upstairs. (This will also help prevent a tree from uprooting your foundation as it grows.)
Think at the ground level, too. A tangle of shrubs near a door can create lurking places for thieves. Keep shrubs trimmed short, or plant perennials there instead. Don't forget the back entry -- many thieves look there first. If there's no convenient hiding place, thieves will generally look for an easier target down the street. Find out how to use rocks and stones strategically in your landscape plans.