A member of the German wireless police picks up signals on the radio equipment he carries on his back, while his colleague takes notes. (Photo by General Photographic Agency/Getty Images). Circa 1925

Tara West signals to her partner Natalie Cook during the Bronze final match during the Australian Beach Volleyball Championships at Glenelg Beach on March 13, 2011 in Adelaide, Australia.

People wear masks to help guard against the Coronavirus in downtown Tehran, Iran, Sunday, February 23, 2020. On Sunday Iran's health ministry raised the death toll from the new virus to 8 people in the country, amid concerns that clusters there, as well as in Italy and South Korea, could signal a serious new stage in its global spread. (Photo by Ebrahim Noroozi/AP Photo)

The Haʻikū Stairs, also known as the Stairway to Heaven or Haʻikū Ladder, is a steep hiking trail on the island of Oʻahu. The trail began as a wooden ladder spiked to the cliff on the south side of the Haʻikū Valley. It was installed in 1942 to enable antenna cables to be strung from one side of the cliffs above Haʻikū Valley to the other. A building to provide a continuous communication link between Wahiawā and Haʻikū Valley Naval Radio Station was constructed at the peak of Puʻukeahiakahoe, elevation about 2,800 feet (850 m). The antennae transmitted very low frequency radio signals from a 200,000-watt Alexanderson alternator in the center of Haʻikū valley. The signals could reach US Navy submarines as far away as Tokyo Bay while the submarines were submerged.

A dancer from the Trisha Brown Dance Company performs during “Roof Piece” above the High Line park June 9, 2011 in New York City. Roof Piece (1971) consists of nine dancers performing improvised movement signals to each other in a chain on various rooftops overlooking the city. This presentation marked the first full performance of the piece since 1973. (Photo by Mario Tama/Getty Images)

Kendall Jenner attends the screening of “Girls Of The Sun (Les Filles Du Soleil)” during the 71st annual Cannes Film Festival at Palais des Festivals on May 12, 2018 in Cannes, France. (Photo by Stephane Cardinale/Corbis via Getty Images)

Cast members from “Michael Jackson ONE by Cirque du Soleil” perform during the 2017 Miss USA pageant at the Mandalay Bay Events Center on May 14, 2017 in Las Vegas, Nevada. (Photo by Ethan Miller/Getty Images)