In "Men in Black", what device is used to erase witnesses' memories?

In "Men in Black," the device used to erase witnesses’ memories is called a Neuralyzer.

The handheld Neuralyzer is one of the Men in Black organization’s essential tools for keeping alien activity secret. After an agent points it at a witness, a bright flash erases or alters the person’s recent memories. Agents then provide a harmless explanation for what the witness saw, helping the organization maintain its cover and protect the extraterrestrial community living secretly on Earth.

The Neuralyzer is not the same as the MIB’s firearms, which are used against threats such as hostile aliens. "Flash Gun," "Memory Eraser," and "Mind Wiper" describe the device’s function informally, but none is its canonical name. In the first film, Agent K uses one on border patrol officers and later on people who encounter MIB operations.

The franchise also features deneuralization technology, which can restore memories in special circumstances. Agent J’s recruitment involves both memory manipulation and the abandonment of his former identity.