The alarm klaxon, or base alarm, is a mechanism that is installed in Stargate Command.
The alarm klaxon has three blaring modes: a high-pitched mode used for unscheduled off-world activations, a low-pitched mode used for internal conflicts, and a slow low-pitched mode used for the self-destruct countdown. Several types of alarm klaxons exist, including stationary klaxons, vibrating klaxons, and spinning klaxons. All types of klaxons, except for the vibrating klaxons, can illuminate the immediate area. (SG1: "Sight Unseen")
The embarkation room of Stargate Command contains two spinning klaxons, one next to each exit door; additionally, two vibrating klaxons exist on either side of the Stargate. Two stationary klaxons exists in the control room, one above the gate technician's head, and a second one, strangely blue coloured on the wall opposite the star map near the stairwell to the gateroom access door. Stationary klaxons are found throughout the rest of the base. Additionally, a number of klaxons seem to work when the SGC's main power is down; thus, the klaxons are powered by the base's auxiliary power system. (SG1: "Shadow Play", "Sight Unseen", "Metamorphosis", "Lockdown", "Revelations")
The alarm klaxon is automatically activated by a program each time the Stargate receives an incoming wormhole. The klaxon can also be manually activated through a klaxon button in case of an emergency. To differentiate between off-world activations and internal conflicts, the button is designed to activate the production of a lower pitched sound. When the base's self-destruct is activated, a slower, lower-pitched sound is produced by the klaxons. If the base's power is ever lost, the spinning and stationary klaxons serve as mechanisms of illumination for the base personnel. (SG1: "Shadow Play", "Sight Unseen", "Lockdown", "Revelations")
- Atlantis has a similar alarm system that was built by the Ancients, though it is only heard when the self-destruct is activated.
- The name of this mechanism is given in both the closed captions and transcript for the episode "Shadow Play." The term is a generic name used to represent a brand of vehicle horns.