Don’t have an old the Amazon Kindle Fire 7? You can purchase a new one for $49.99 at http://goo.gl/PCFI5W. That’s much cheaper than a normal security camera and it works better than any other $50 security camera besides!
Other, more expensive, Fire tablets are available from Amazon but you won’t need any of them if your sole purpose is to add a video monitor to your home. The $49.99 model will do everything you want for that purpose.
You will need to have wi-fi networking in your home to make it all work.
You can download the FREE SalientEye Home Security Alarm app at https://play.google.com/store/apps/details?id=com.mantishrimp.salienteye&hl=en
You will need some sort of stand to hold the tablet in a vertical position to let it monitor a room. There are probably a thousand ways to do that. Perhaps the easiest way is to purchase a book stand, often called a cookbook stand, at Wal-Mart or Bed Bath and Beyond or most any other department store or bookstore. Inexpensive book stands often sell for less than $10.