On my department's system...
Pushing the man down, or emergency button, causes a signal to be sent to the dispatch consoles monitoring that talkgroup/channel. We also have a link to our CAD system that will pop up a huge (800x600) dialog box on our screen linking your emergency button on your portable to whatever truck that portable is assigned to. (So if your portable shows assigned to 23 Pump, we get "!! EMERGENCY !! - 23P" on our screen.) This alert goes to all CAD stations whether they are responsible for that rig/district or not. As well, our system will pinpoint the location of the truck if it's not on a call, and create a call for that exact location (via GPS).
ALSO..
Your microphone will become "hot" (open) for 15 seconds after your button has been pressed. Dispatch, and everyone else on the channel, will hear anything in your general area (usually on our system this is "What the hell..? Why is this stupid thing beeping--"
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).
As I say, this is how it works on
my department's radio system. They vary widely; some systems don't have a hot mic after tripping emergency. Some systems 'freeze' the radio display and sound so that anyone near you will not be aware you have triggered your emergency alarm (good if it is a hostile situation).
Some radio systems even have a device to be clipped to the radio that will trip this alarm if the radio is on its side for more than x number of seconds (i.e. if the person holding the radio has been taken down).
Hope this helps...
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