ALARM (Air Launched Anti-Radiation Missile) was developed to fill a requirement for an advanced defence suppression weapon for SEAD missions. Rather than deploying a dedicated SEAD platform the RAF preferred each aircraft to have its own defence suppression capability. ALARM is a self-contained fire-and-forget system, with an added loiter capability conferred by a parachute.
In loiter mode, ALARM will climb to a higher altitude on launch. If the target radar shuts down, the missile will deploy a parachute and descend slowly until the radar lights up. The missile will then fire a secondary motor to attack the target.