An ADT (or similar) security system is going to cost you $300-500 to install, and $40/month. Since most households who can afford such security systems likely already have broadband, always-on internet, and the members likely have smartphones with data, it is possible to offer a cheaper alternative that builds on services they are already paying for. Any hardware for the system could also be built using standard "off-the-shelf" components.
Off the top of my head, I can imagine instead of hardwiring door/window sensors, motion detectors, cameras, and microphones you could connect them all via wi-fi. And instead of having a 24 hour monitoring center, you could have a cloud-based app that routes alerts directly to the owner's smartphone.
This way, the $500 of equipment become $100, and the $40 monthly monitoring fee becomes $10.
How does the ADT system work? Some kind of dedicated line?
I think for the younger generation, alarms with phone line connections won't work anyway. Over half of my friends/coworkers don't have a landline phone. But they all have smartphones and broadband. Companies will have to find a way to have a reliable system that works with broadband.
the easy part is setting up a callcenter to handle the alarms going off. You probably also need to coordinate with local police departments so they know what is going on when they get a call from you. (alternately, you could contract with local private security firms.)