You would be surprised at the number of people that have recorded CCTV coverage of their homes. It used to be more common at the very high end and those engaged in illegal enterprise, but has filtered up and down to regular people. I've seen an increase in the amount of overt vs. covert systems in the past few years.
The upside is that you might be able to use it as evidence against someone tht is doing you harm. The downside is that the same sysyem might be used against you, should you have to defend yourself. Most of the time you'll be fine, and you'll get the benift of the doubt, but nothing is 100%.