Looking at the effect of interference from just a wireless headset,consider how simple it would be to have an intentional generator for interference to render all of the sensors ineffective. So the task of defeating a 2.4 GHz wireless system is almost trivial. But consider the effort to disarm even one properly wired sensor. So why waste time with a product that is so very easily defeated?
Cabe, that sort of interference certainly happens in voice communications systems, so it could also happen in a data system. Frequency hopping through a wide rangee could help, but that adds a lot of cost and certainly would increase the battery consumption quite a bit. Of course, DARPA probably has a work-around solution that they are not talking about much.
If the control panel has not heard from a sensor, due to interference or whatever, that triggers an alarm, so the real issue becomes false alarms from interference. That suggests the system is best suited for rather short distances, but at least it would be very easy to set up.
What better way to nullify the effectiveness of a security system than to make it deliver false alarms several times a day. And a transmitter able to do that could be quite small and easily hidden.
Of course the convenience of a wireless installation may be the overwhelming motivation for some folks, but in my opinion the reliability of a security system trumps easy installation by a large margin, and even trumps minimum cost by a fair amount. What good is an alarm system that is not working? It serves Only as a deterrent until the bad guys find out.