And how does the device snug in its little box tell the difference between the transponder being off in a parked aircraft or the transponder losing power during level flight or after a gentle ditching.
Assuming the device was a GPS combined with a transmitter, than I guess it can determine if the aircraft is parked or flying.
Seriously however, I do take your point. This needs to be thought through very carefully. As you say, simply adding a new device without thinking through all the issues will lead to unintended consequences.
But many people think we need to do better. Given all the double and triple redundancy on aircraft today, it seems very odd that geolocation remains so primitive and so fallible.
Given current technology, is it acceptable that an aircraft disappears when out of range of secondary radar (AF447), or gets into trouble and disappears off radar when it descends below the horizon (Air Asia) or disappears after a transponder is turned off (MH370)? Is any of this acceptable?