There was an article where they interviewed a bunch of burglars and asked them the best way to secure your house. First they listed off all the things that don't work, like alarms and cameras. Then they said:

- Number one, have a TV on. If they see a TV on they assume people are home and watching.

- Get a big dog. If they have to choose between a house with a dog and one without, they'll chose the one without.

- Get motion activated security lights. Always-on lights just provide extra light for breaking in, the motion sensors draw attention (although most robberies happen during the day so it's sort of a moot point).