A hundred years ago this month, there might not have been a spy behind every tree. But there very well could have been German spies using those trees to conceal secret antennas, and the editors of Electrical Experimenter, in the September 1917 issue, were doing their public duty to warn Americans of the potential threat. Some possible secret spy antennas are shown here, along with the warning:

In preparing this article we have endeavored to show the unsuspecting
public how an enemy agent may either send or receive radio messages
by means of the most innocent appearing objects.

The Editors thought it best to give the article wide publicity, in order
that patriotic citizens may the better apprehend possible spies, who might be using secret aerials of the types illustrated.

The article is intended for public enlightenment, as well as for the
country’s safety.

According to the article, there could be a spy cleverly using your shade tree as an antenna, and it was a good idea to go out and check: “Have you examined your shade trees closely this summer? Don’t be surprised if you find a wire cleverly painted to match the bark on the tree and leading up to the various branches. It is readily possible for a persistent member of the enemy espionage squad to thus rig up a tree areial, and it is not necessary to travel very far to find a sufficiently large tree, which would serve as a framework for several hundred feet of insulated wire.”

A similar warning was warranted for those hanging their laundry out to dry: “If you live in the city (or even in the country) and have occasion to use a metal clothes-line of any appreciable size, it might pay you to closely scrutinize the supporting framework to see whether or not some alien enemy has been at work in an effort to use it for wireless communication purposes.”

These spy antennas could be anywhere, as shown in the illustration above.

Elsewhere in the same issue is the report of the U.S. Government blowing up the wireless tower at Shoreham, Long Island, erected at the cost of $200,000 by Nikola Tesla some twenty years earlier. The structure was no longer in use, but “during the past month several strangers had been seen lurking about the place.” Those lurking strangers could very well have been German spies, hanging around the 185 foot tower to use it as an antenna to contact Germany. Therefore, the Government blew it up.