Mac: There are all sorts of ways to make your own home security system. If you're looking for something simple and cheap, Macworld shows off how to use your Mac's camera as a DIY security camera using nothing but an Automator workflow.
The basic idea here is that your Mac will use your camera to take a screenshot every minute or so. Using an Automator workflow and a calendar alarm, you set it up so your Mac shows you what's happening in your room and then uploads that to iCloud so you can check in from anywhere. Your Mac has to be on the entire time, and it's certainly not the most secure system in the world, but it gets the job done for free. Head over to Macworld for the guide to making the script for yourself.