A Teslascope is a radio transceiver that was alleged to have been invented by Nikola Tesla for the purpose of communicating with life on other planets. Even though Tesla talked about “interplanetary communication“ on many occasions, it has never been confirmed that he built such a device. The paranormal device called the Hyperdimensional Oscillator is sometimes associated with this device
The claim that Tesla created a device called a “Teslascope” grew out of Arthur H. Matthews 1970 book, "The wall of light; Nikola Tesla and the Venusians space ship, the X-12" (OCLC 2094500). Matthews, who had apprenticed under Tesla at the turn of 20th the century and worked for him until Tesla's death in 1943, wrote that Tesla had designed it in order to communicate with extraterrestrials. Matthews made many other claims, such as Tesla was born on Venus (supposedly told to him by Venusians who visited Matthews in Canada). Matthews also claimed that he built a model of a Teslascope in 1947 after Tesla’s death and operated it successfully, although it is hard to verify such a claim since Matthews left unclear documentation of his accomplishments.
Tesla had mentioned many times during his career that he thought his inventions such as his Tesla coil, used in the role of a "resonant receiver", could communicate with other planets. In 1896, Tesla told interviewers:
The possibility of beckoning Martians was the extreme application of [my] principle of propagation of electric waves. The same principle may be employed with good effects for the transmission of news to all parts of the earth....Every city on the globe could be on an immense circuit. [Thus] a message sent from New York would be in England, Africa and Australia in an instant. What a grand thing it would be.
In 1899 when Nikola Tesla was investigating atmospheric electricity using his receivers in his Colorado Springs lab, Tesla observed repetitive signals of what he believed were Extraterrestrial radio signals that were substantially different from the signals he had noted from storms and Earth noise. Specifically, he later recalled that the signals appeared in groups of one, two, three, and four clicks together. Tesla seemed to think the signals were coming from Mars. Research has suggested that Tesla may have had a misunderstanding of the new technology he was working with, or that the signals Tesla observed may have simply been an observation of a natural radio source such as the Jovian plasma torus signals. In 1901 Tesla said the following about his 1899 Colorado experiment:
I can never forget the first sensations I experienced when it dawned upon me that I had observed something possibly of incalculable consequences to mankind..… Although I could not decipher their meaning, it was impossible for me to think of them as having been entirely accidental. The feeling is constantly growing on me that I had been the first to hear the greeting of one planet to another.
[I have conceived] a means that will make it possible for man to transmit energy in large amounts, thousands of horsepower, from one planet to another, absolutely regardless of distance. I think that nothing can be more important than interplanetary communication. It will certainly come some day and the certitude that there are other human beings in the universe, working, suffering, struggling, like ourselves, will produce a magic effect on mankind and will form the foundation of a universal brotherhood that will last as long as humanity itself.—Nikola Tesla,