Since this also admits light to the lower areas, this section can be planted with a groundcover, or lower growing plants. Around the most vulnerable windows, consider planting thorny or prickly plants. If the area is shaded, try mahonias. Wind chimes create delightful sounds when wind passes through them. But they might also startle an invader, and alert you, if placed along entry pathways.
Motion detectors are available in cute forms that make animal sounds.
Others take the form of lights that come on when someone passes by or sprinklers with swivel heads that send out hard squirts of water aimed at the triggering motion. These aren't harmful in themselves, but they might disconcert a potential invader enough that he will move on to another house. RCW Nurseries urges customers to take a good look at their outdoor lighting at night. If none exists, consider installing some. Darkness is probably the single most inviting element to a potential burglar.