Electronic devices like the GEM and Scott's Pack Tracker are an attempt to be an accountability system, a PASS, and an electronic recall system, all at the same time.
They have some inherent problems, especially with signal attenuation in large structures. This can keep them from working properly. Like any electronic device, they can fail.
The best accountability systems are simple, organized, and work when the electricity doesn't.
"red for exterior"?
What, people actually have exterior firefighters? :-)