One hundred years ago this month, the July 1921 issue of Science and Invention proposed this idea of an early tracking device to prevent kidnappings. The photograph in the lower right hand corner served as the inspiration, as it showed a baby carriage equipped with a receiver to play lullabies sent by nearby amateur stations.

The magazine editors took the idea a step further and proposed a transmitter and tracking device, so that the kidnapper could quickly be brought to justice.