"The Microvision was the very first hand-held game console using interchangeable cartridges. It was released by the Milton Bradley Company in November 1979. The Microvision was designed by Jay Smith, the engineer who would later design the Vectrex gaming console. The Microvision's combination of portability and a cartridge-based system led to moderate success, with Smith Engineering grossing $8 million in the first year of the system's release. The hand-held also appeared in the movie Friday the 13th Part 2. However, very few cartridges, a small screen, and a lack of support from established home video game companies led to its demise in 1981."
Source: Wikipedia, "Microvision", available under the CC-BY-SA License.