Harry Vanderspeigle's device is a device of alien origin seen on the television series Resident Alien. Owned by the alien who assumed the form of Harry Vanderspeigle, it has the power to kill every human on the planet Earth but leave all other life intact. It can also be used in a more targeted fashion to vaporize or simply knock out individual humans.
Harry Vanderspeigle's device is a spherical object, small enough to fit into the palm of one's hand. It glows a neon green when powered up and is somehow tethered to Vanderspeigle's spaceship. The surface features a black pattern of triangles and pentagons. The apparent sole purpose of the device is to completely eliminate the Earth's human population. When activated, the device emits a green wave which spreads out in all directions, instantly and completely vaporizing the body of human it comes into contact with, though leaving their clothing intact.
When Harry Vanderspeigle crashes his spaceship on the planet Earth, he loses both the device and the spaceship. He then spends many months searching for both in the snowy mountains of Patience, Colorado, but is unable to find either. Eventually, facing failure, a telepathic conversation with an octopus leads him to realize a potential solution, enlisting the help of the boy Max Hawthorne who is able to see through his human reconstruction to the alien beneath. He realizes that the same power also allows Max to detect the "green glow" given off by alien technology. Using this power, he tracks his device to a glacier, where he is confronted by Asta Twelvetrees and D'Arcy Bloom, the latter of which had previously warned him away from the glacier due to the danger.
Before Vanderspeigle can recover his device, a crevasse opens up and swallows them all. After they wake from the fall, Vanderspeigle moves to hide his device, but a deeper crevasse opens up, causing him and Twelvetrees to fall even further. In the second fall, the device is apparently damaged and loses its glow. In the fall, Vanderspeigle is injured and his alien form starts to show through, and he is forced to reveal his alien nature to Twelvetrees. He also explains that he is searching for his device, but he claims that it is a "radio" that will allow him to contact his people in order to get Twelvetrees to search for it. Bloom eventually rescues the group, but Vanderspeigle, badly injured and despairing the loss of his device, tells Twelvetrees to simply let him die. Twelvetrees then reveals that she actually managed to recover the device, so he tells her what she must do to save him: cut off his injured leg, which is poisoning him.
While recovering from his injuries and regenerating his leg, Vanderpseigle is paid a visit by Max. Max asks if he found his "radio," and Vanderspeigle shows him that the device has lost its power. The two of them are joined by the girl Sahar, who suggests that he try the local hardware store for the part that he needs to fix it. He, however, tells the two of them that he's out of luck unless they know somebody else who has encountered extraterrestrials. Max then tells him that he knows where he should go if he wants to find "alien stuff." With Twelvetrees help, Vanderspeigle visits a "UFO Con" in New Mexico, looking to find someone who has previously been abducted by Grey aliens and implanted with a tracking device. He discovers a likely candidate during a panel of "alien experiencers," but hits a dead-end when the woman turns out to have been lying about having been abducted by aliens. Vanderspeigle is then pursued by the host of the panel, Peter Bach, who turns out to have the same ability as Max to see through Vanderspeigle's human disguise. Vanderspeigle lays a trap for the man and then discovers to his delight that Bach himself is carrying the needed implant. Ignoring Bach's pleas, he cuts it out of him.
With the needed technology, Vanderspeigle is able to restore his device to full functionality. He, however, finds himself having doubts about his mission. Considering the matter, he decides it might be a good idea to test the device first, by using it in a more limited functionality, in which it can send out a targeted pulse. He decides to use it to dispose of the corpse of the human Harry Vanderspeigle, which has been troubling him since he killed him and assumed his form. Before he does so, however, he has a hallucination of the corpse, who tells him that he's just stalling and that he's been infected with humanity. He shouts that he doesn't have to listen to that and dismisses the hallucination, then activates the device, vaporizing the body. In the process, however, he is shocked to discover that the small portion of him which came into contact with the device's wave has been damaged. He realizes that if he is still on Earth when the device goes off, then he too will die.
Asta Twelvetrees then enters his cabin and confronts him with her knowledge of the truth - that he killed the human Harry Vanderspeigle. He tries to salvage the situation, but she tells him that it is unforgivable and that she never wants to see him again. She tells him that they are not friends and leaves. He sobs, saying that he thought she was his friend and declares that he no longer likes this place. He pushes the button on his device, activating a 90 minute timer. He then makes for the facility where his spaceship is being held and repairs the ship, knocking out the agents who come after him and preparing to launch it. However, as he does so, the agents bring forth Twelvetrees, as well Max Hawthorne, who have come to try to talk him down from killing everyone on Earth. Shocked to see them, he lowers the ship to the ground and blasts the agents that are holding the two captive. Twelvetrees shouts at Max to run and hide.
Twelvetrees then talks with Vanderspeigle, telling him that she knows he's changed and that he's not who he was when he killed the human Vanderspeigle. She pleads with him not to kill everyone, saying that she is his friend. He replies that if she's his friend, then they'll go to his planet and kill everyone together before leaving. She tells him that she's not leaving, that she's staying there, and he replies that he won't kill everyone. The two share a tender moment and Vanderspeigle tells he has to go, or else his device will kill everyone in 80 seconds. He takes off on his spaceship, leaving Twelvetrees in wonder as it teleports away. Once a safe distance from the Earth, he detonates the device harmlessly in space. Max then reveals that he has stowed away on the spaceship.
Harry ends up crashing back to Earth with Max on board. Discovering that his spaceship is totaled, he converts it to a survival kit of "alien balls," hoping to live out his life as a human on Earth. The octopus, however, reveals that since he did not complete the job, his people will likely return to do instead using a similar device. Later, however, he learns in a message from the alien Goliath that his people will not be coming, as another alien species is already on Earth and planning to take it over.