Pressing the red button on the Multiface raised the non-maskable interrupt line on the computer's processor, effectively taking control of the computer. The Multiface would then page in its own ROM, temporarily replacing the computer's operating system with that within the Multiface.
The Multiface One was released in 1986 for the ZX Spectrum 48K. It initially cost £39.95 and had the capability of saving data to cassette tape, ZX Microdrive, Opus Discovery (an external 3.5 inch disk drive) or Technology Research Beta (an interface that allowed 5.25 inch and 3.5 inch drives to be connected). The device worked on 128K Spectrums, but only if they were put in 48K mode. It featured a Kempston joystick port, and later revisions contained a switch that effectively 'hid' the device from software. Early versions had a composite video out port but this feature was later removed.
The Multiface Two was released for the Amstrad CPC 464 and had similar features to the Multiface One.
The Multiface 128 was released in April 1987 for the 128K version of the Spectrum, including the original +2 model. It worked in 128K or 48K mode and it existed in two versions; initially without a 'thru-port' and later, with one, both of which originally cost the same £44.95, but were later reduced to the same price as the Multiface One. The 128 introduced the ability to save to the +D and DISCiPLE disk systems, but lost its joystick port. The device was not compatible with the later Spectrum +2A or the Spectrum +3.