Found on Guns.com: The AMT Backup in .45 ACP

Arcadia Machine & Tool, better known as AMT, was a niche firearms manufacturer from Irwindale, California. Perhaps best known for the Automag series of pistols, ranging from .22 WMR up to .50 AE, AMT produced interesting guns. The Backup was a no-nonsense pistol that proved to be one of their more popular models. The gun's intent is in the name -- to serve as a backup gun, mainly aimed at the LEO market. The marketing slogan was “The smallest and most powerful backup weapon available." That must have stuck because there are a lot of these guns floating around the used market.