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Since it's possible to call 911 from an old inactive cell phone, would it be possible to design a RF transceiver that could make 911 calls without any sim card or monthly mobile plan? Or does such device already exists?
EPRB for maritime use or PLB for hikers are probably the terms you want, they transmit position and a serial number to a rescue coordination center (In the EPRBs case the serial number is registered to a particular vessel, not sure how that works for PLBs).
Neither relies on the cell phone network as they tend to be used outside reliable coverage, instead using 121.5MHz (Aircraft emergency frequency) and a UHF transmission that is looked for by some satellites.
These are not capable of voice transmissions, and are purely narrow band data transmitters (No reception capability apart from the GPS used for position reporting).