Carrier: The system, or variants of it, already works well on both military (rotary and fixed wing) and VIP fleets but the fact is that cost and ease of maintenance considerations are different for commercial airlines.
Whatever any of us would like to think, the impact on cost per seat mile flown will be the primary consideration for the bean counters at any airline. Fitting the system to operational passenger aircraft is the only way of checking the actual impact on finances through any increase in drag or weight, the robustness of the systems in day-to-day commercial operations and ease of maintenance by line engineers away from base.
You are right to suggest that false alarms would be problem, but this is well understood by the manufacturers, true for any aircraft (albeit to a differing degree) and may not be the issue you think it is.
The threats are understood from current military operations in various parts of the world and are largely from man portable shoulder launched missile systems, of the type this system is designed to counter. It would surprise you just how easy it is to acquire one of these system, which I understand can be effective up to >10,000ft, hence the Department of Homeland Security's programme.
More generally, I live in the hope that the boffins involved are doing everything possible to keep one step ahead of those characters on the other side that spend their time trying to do the same.