This young woman is mystifying her friends by carrying on a conversation with this black box. Close inspection reveals that the box is, indeed, empty, but voices manage to emanate from it.

Actually, she’s talking to an accomplice in another room, and inside the box is a one-transistor amplifier concealed in a false bottom. It contains a pickup coil, consisting of 2000 feet of #30-34 wire. This is the secondary of an audio transformer, the primary of which is concealed under the carpet.

The two-way capabilities were courtesy of a hidden microphone in her room. The accomplice would hear her voice, and talk back through the box. The whole system is described in the June 1960 issue of Popular Electronics.

For those who don’t like winding the coil themselves, a suitable replacement would be a telephone pickup coil, similar to the one shown at left.