If you have an indoor cat, make sure he is "stimulated". The new buzz word is environmental enrichment. This means to make sure that your cat has opportunities to have an interesting life while living inside.
You an do this by providing toys, a screened in porch, a bird feeder for them to watch as well as scratching posts and cat trees.
For more information on enriching your cats environment, please read Selecting the Right Environmental Enrichment for Your Cat