Eighty years ago, this west coast air raid warden was subject to call at any moment, but he might need to be somewhere in his house other than next to the telephone. His solution was to use something called an “electric sentry” to alert him.

As near as I can tell, an “electric sentry” was a one-way intercom, which used the house wiring to transmit the signal. The transmitter was plugged in near the telephone ringer. He could then carry the receiver to another room in the house, or even a neighbor’s house, with the assurance that he would hear the ringing phone.

Here, he appears to have the sentry receiver nearby while he repairs a radio. His daughter assists him by trying on his warden’s helmet. The transmitter is shown at right.

The item appeared in the May 1953 issue of Popular Mechanics.