A lock-out device is a system used on game shows, particularly trivia shows, to determine in real time which contestant has activated their signal first. The system is designed to detect the first signal(s) it receives and ignore subsequent signals. The system provides some indication of which contestant has signaled, such as a light for each contestant, allowing the relevant parties to clearly determine who has signaled first.
The device used by a contestant to send a signal to the lock-out system is called a signaling device (or more commonly a buzzer, perhaps due to the sound some early devices used to indicate signaling). They are typically a button on a hand-held cylinder or mounted on a podium in front of the contestant. The act of signaling is commonly called ringing in, or buzzing in.
Lock-out devices were not always mainstays in game shows. Early game shows lacked this technology, and those that required it made use of alternate, less-precise, systems. For example, the 1969 game show He Said, She Said required contestants to raise their hands, while the host and production staff determined visually which had raised their hands first. A similar, but more technical system was actually used in the earlier game show Winner Take All; the show was one of, if not the first applications of this forerunner of the modern lock-out. On the show, two contestants competed at answering trivia questions, with the first to ring in earning the right to answer. However, the technology was not yet developed for a lock-out system. Instead, each contestant's hand signal sounded a different sound effect (a buzzer and a bell, perhaps influencing the future terms of ringing or buzzing in). Whichever was deemed to have sounded first was considered to have control. A modern lock-out device essentially utilizes some sort of electronic system to do the determining with precision and certainty, rather than by human observation.
In general, though, a majority of early multi-player game shows - even those dealing with trivia - simply lacked the gameplay element of pitting contestants against each other simultaneously. Competitive game shows instead took to having contestants alternate turns, such as in Twenty One, Pyramid, and Password.
Perhaps the most famous modern game show to use a lock-out device is Jeopardy!, which uses a sophisticated system that is so fundamental to the game, mastering the signaling device is commonly said to be as or more important than knowing the answers to the questions. On Jeopardy! (and its various spinoffs), the lock-out device has several advanced features. When the host finishes reading the question, a production assistant activates the lockout device, and the border of the game board lights up (which home viewers don't see). Only at this point are contestants allowed to ring in. If a contestant rings in before the system and lights are activated, their signaling device is deactivated for a fraction of a second. Poor performance has been regularly blamed on failure to master the lock-out system, and on celebrity editions, celebrity contestants have been known to jokingly claim their signaling devices to be broken.
In 2000, sister show Wheel of Fortune, aided by a new computerized video board, introduced a segment called "Toss-up Puzzles" which introduced lock-out devices to that show as well. In these short rounds, contestants would have to ring in to guess the answer to a puzzle whose letters were randomly revealed one at a time until solved. Currently, three of these rounds are played per show, with two of them determining who will start play in the subsequent standard round.
Other lock-out devices can have more complex operations. On the 1975 game show Split Second, the device determined the order in which the players signaled; in the show's revival in the 1980s, the order is displayed on the front of the contestant podiums (a 1, a 2, or a 3). In a similar vein, on Crosswords, the two competing contestants are joined in the second round by three "spoilers" who can replace one of the main contestants if they ring in and answer correctly. However, the two main contestants are always given an opportunity to answer first if they ring in, even if it is later than the spoiler. This results in a five-way system in which the order of ringing in is displayed on the front of each podium, 1 or 2 on the main contestant's podiums, and 1, 2, or 3 on the spoilers'. Should all five players ring in on a question, the host can ask each of the main contestants for an answer in the order they rang in before moving on to the spoilers in the order they rang in (should no one provide the correct answer) by using the numbers on the podiums.