Lifeline, released in Japan as Operator's Side,[a] is a 2003 survival horror adventure video game developed and published by Sony Computer Entertainment for the PlayStation 2.

Lifeline's defining aspect is its voice user interface: the vast majority of gameplay is conducted by using the PlayStation 2's microphone to issue commands, which are interpreted by the game via speech recognition to control Rio and dictate her movements and actions.

However, Lifeline still sold well enough to be rereleased in Japan on September 25, 2003 under Sony's The Best budget range, and the game has maintained somewhat of a cult following over the years since its release for its innovative gameplay and the depth of its voice mechanics.

Lifeline is a survival horror adventure game where the player issues orders to Rio Hohenheim as she attempts to escape a monster-infested space station.

The player can play games with her (e.g. challenge each other to tongue twisters, with Rio receiving health if successfully completed), ask her to do sexual things (e.g. to "do a sexy pose", which she may or may not follow through with), or simply engage in small talk with her (e.g. suggest she eat food or shoot at a static object; she may do so, or more commonly explain her rationale for not doing so).

Suddenly, unidentified alien-like monsters attack the festivities, killing most of the guests and staff and separating Naomi and the Operator, who is trapped in the Space Station Hotel's main control room.

From the control room, the Operator, having full access to the Space Station Hotel's mechanisms and cameras, comes into contact with Rio Hohenheim (voiced by Mariko Suzuki in the Japanese version and Kristen Miller in the English version), a cocktail waitress who survived the initial attack after being locked in a holding cell for her own safety and is attempting to contact the control room.