For other meanings of "Lifesigns", please see Lifesigns (disambiguation).

A life sign or bio-sign is a signal or collection of signals given off by a lifeform that indicates that it is currently alive, or functional. Upon approaching another starship or a planet for which they had limited intelligence, starships usually performed a scan for life signs. This information became part of the bridge crew's determination as to whether to board the ship, send a landing party, or carry out any other action.

The USS Kelvin was designed to track its crew member's life signs. When Captain Richard Robau was murdered in 2233 of an alternate reality, the computer signalled his termination. (Star Trek)

Dr. Juliana Tainer was a Soong-type android that was designed to give off Human life signs. (TNG: "Inheritance")