Home security systems that can detect motion, make recordings, and then contact you to deliver the news, are not exactly cheap. Even if you set up a home configured system you're still going to have to spend some cash.
But if you have one or more old Android handsets floating about you could set up a little motion detection system of your own. When the handset camera detects motion it can sound an alarm, capture stills and send them to the cloud, and send you an email or SMS. A link in the email takes you to the photos that were taken.
The disarm password is important – and if you really take to this app and set up several old Android handsets, then you'll need to disarm them all when you're at home for obvious reasons. I feel like using Salient Eye to find out which of my neighbour's darned cats is coming in overnight and stealing kitty's food.
Product: Salient Eye