My take on 4E is that you can pretty much do anything your imagination and the DM allows. It doesn't matter that there's no way to dispel a ritual in the PHB; you have the tools to resolve that action.
The question is, I guess, as DM, how do you see this working in your setting? Is it possible, or not? If it is possible, how does one do this - do they need a ritual or will a skill challenge work? What about using the power Dispel Magic out of combat, as part of a skill check? (Think of Dispel Magic as a tool that you need to get the job done.)
I would personally go with a skill challenge, setting the level of the challenge equal to the level of whoever created the Eye of Alarm. I would also allow a single check with Dispel Magic.