Basically, to turn your old android Smartphone or tablets into a security camera that allows you to live stream remotely, record and receive motion alerts, you need an old android phone or tablet with functional rear or front camera, a security camera app for android (android cell phone security camera app) to turn the android phone to a webcam
If a land line is cut and your home security depends on it, your security system is now useless. A wireless system resolves that issue. The second reason is convenience. Just like you have a cell phone to maintain communication on the go, with a wireless home security system, you can access and communicate with your system while on the go.