This Plectron is a specialized FM single channel emergency alerting radio receiver. It is used to activate emergency response personnel, and other disaster warning systems. These radios were manufactured from the late 1950s, through the late 1990s by the Plectron Corporation in Overton Nebraska. Many hundreds of thousands of these radios were placed in homes of first responders across all of North America. This included ambulance crews, full-time and volunteer firefighters, off-duty specialized police response teams, Civil Defense members, and search and rescue teams.
A Plectron's main feature (distinguishing it from a regular squelched radio) was its selective de-squelching. It would only sound when a correct pair of tones were broadcast allowing many agencies with different tones to share the same frequency. Very similar to a Continuous Tone-Coded Squelch System or CTCSS.
The power source needs to be 117 volts AC at 60Hz and at least 5 amps.
The Motorola MINITOR pager also used this function and have now largely replaced the Plectron.