Machine lure is the term used to refer to devices in Horizon Zero Dawn that emit a machine-attracting signal. They produce a signal with an unknown, though presumably wide range that summons machines.
A machine lure is small enough to be held in the hand. It is cylindrical in shape, with a red, blinking beacon-like light, and produces a pulsing noise at an interval of approximately once per second. Any machine within an unspecified radius of the device is drawn to its location by this signal. The precise nature of the signal is not known.
The origin of machine lures is unknown, and it is not clear if all machine lures stem from a single source or are ad-hoc devices created independently.
The Oseram Warlord Dervahl had a number of machine lures in his possession. He had them at a workshop high in the mountains northeast of the Oseram freehold settlement Pitchcliff. The Carja trader Shahavad discovered the workshop's location. He had a regular clientele of Carja nobles interested in ancient artifacts, and took one, intending to sell it to one of them. However, he was unaware of the device's nature, and accidentally caused Glinthawks to incessantly attack Pitchcliff when he took it there. The Nora huntress Aloy found him desperately trying to turn it off. She destroyed it and, on learning of the workshop's location, went there and destroyed the others. Dervahl himself subsequently used a machine lure to attract Glinthawks against Aloy when she foiled his attempted terrorist bombing of the Carja capital Meridian.
The Carja criminal Ranaman used a machine lure to summon machines to his father's estate, where they killed all present except his sister Daradi, whom their father locked in a room to preserve her life when the machines arrived and attacked. Ranaman subsequently attempted to kill Aloy and Daradi by using the lure to attract Glinthawks against them, much like Dervahl.
The Oseram trap-maker Rasgrund constructed a machine lure while incarcerated in the Carja prison Sunstone Rock. Having scavenged machine debris found in the fields where prisoners labored, as well as metal components from prison equipment, Rasgrund was able to conceal his tinkering from the guards by hiding the materials on his person. He then used it to attract two Behemoths to the prison; the huge, powerful machines attacked, allowing him to escape.
Finally, the wanderer Sylens used a machine lure to bring three overridden Ravagers with him to the Sun-Ring at the Shadow Carja capital Sunfall when he rescued Aloy, who had been thrown into the ring by the Eclipse leader Helis to be killed in a public execution. The Ravagers covered their withdrawal, attacking and thus preventing pursuit by the two Corruptors Helis had used to corrupt the Behemoth he had loosed on Aloy in the Sun-Ring to kill her.