One device for calling for help is a loud alarm with a switch.
Sometimes, when it is necessary to call, a person is unable to, so it would
be useful to make it voice activated. Also, even a loud alarm can only
be heard in a relatively small area, so something that sends a message
on the internet and to rescue services would be better. Sending the location
is possible is the alarm has a GPS locator. Sound and video can help determine
what kind of rescue is needed and / or if the situation is hopeless at
least make it less likely that this situation will happen again, like a
flight recorder.
A device that could accomplish all of this is a wirelessly networked
laptop with a video camera, microphone and speaker. Eventually a rugged
special purpose device could be made, hopefully small enough that it can
be worn on clothing.
Jerry pointed out that this
device should be good in any danger situation even if the person can't
speak or move so it must have body sensors to measure sweat, cardiac rate
etc... to detect the body's answers to dangerous situations.
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