Hmm, it is a pretty interesting way of using old smartphones, but I think that it is not suitable for outside. Besides, I believe that it is much better to use specialized cameras if you want to b sure that everything is working correctly. I prefer to use security systems like this one https://ajax.systems//. It is a complex of cameras, sensors, and stations that are connected with each other and working great. Long story short, it is the most efficient way to defend your house.