When You're Not Home Set your radio to a weather or all-talk station, and leave it on when you leave the house. Experiment a little bit, and find a volume that you can just hear through the closed door. If you need to, put the radio close to the door. No matter where you put it, the sound from the radio will give the illusion of muffled voices, making it sound like someone is inside. This can be a very effective means of warding off intruders, and can also be maddening to solicitors who are trying to figure out why you're not answering the door.
Some people leave on the television instead, but radios draw much less power.
The television does add the element of altered patterns of light within the house. Timers Light timers are inexpensive, and can be programmed to turn your lights on or off at different times of the day. If you want to get creative, you can even use a light timer for your radio. Use a combination, and it can appear that an entire family is home. Light timers are available at most department or hardware stores, and are available in both outdoor and indoor models.