A dungeon monitor (sometimes referred to as a dungeon master or simply a DM) is a person charged with supervising a playspace (or "dungeon") at BDSM events such as play parties and fetish clubs. These people may be of any sex and may normally identify as any role (dominant, submissive, or switch), but while on duty their authority is absolute. If a dungeon monitor orders a play scene to stop, it must be stopped immediately. Dungeon monitors are usually people with significant experience and/or explicit education in BDSM and safer sex practices, and who also have verifiable training both in BDSM safety practices and first aid techniques. They often wear a special uniform or hat, but there is no standard way of denoting who is a dungeon monitor.
The primary responsibility of a dungeon monitor is to ensure the physical safety of all participants engaging in BDSM play. At private parties, it is typically the host's role to act as a dungeon monitor or to nominate an attendee to serve in that capacity. At public playspaces, the venue typically appoints volunteers or employees for the same purpose. Dungeon monitors are normally not permitted to engage in a scene themselves so that they will always remain an outside and objective observer of other players' scenes.
Almost all playspaces define a set of house rules that list the prohibited activities as well as the default safeword and sometimes even a safe gesture. In addition to monitoring play scenes, dungeon monitors also maintain the dungeon equipment between scenes (if the players themselves fail to do so), performing such activities as cleaning surfaces (possibly with disinfectants), replacing pads, and generally readying a play area safely for its next scene.