Melvin Minton built an alien detector to find aliens.
The detector was built by Minty to detect beta particles. Minty knew that anything that passed through the atmosphere picked up beta particles, so built the detector to locate where large amounts of particles had been, much like a metal detector.
When Gita Chandra saw Androvax in Sarah Jane Smith's driveway, she called Ocean Waters to tell her. Ocean and Minty arrived at the scene and produced the detector. He set it up and switched it on. Sarah Jane commented that he should take it on Dragons Den. The detector started to detect high levels of beta particles, but Sarah Jane used her sonic lipstick on it, stopping him from finding Androvax in her attic. Minty did not understand why it was not working. When Sarah Jane, Rani Chandra and Clyde Langer talked to Ocean Waters about her encounter with Mister Dread, Minty detected Clyde as an alien, as Androvax was inside him. (TV: The Vault of Secrets)