Depolarizer

The depolarizer is identified by Zoe as a wearable device positioned at the back of the neck, capable of jamming the Cybermen’s hypnotic control waves. Its proposal shifts the team’s focus from analysis to urgent action, as the Doctor tasks Zoe and Watkins with constructing it. The depolarizer becomes the team’s primary countermeasure, symbolizing hope amid the global crisis.

Zoe identifies the depolarizer as a wearable device positioned at the back of the neck, capable of jamming the Cybermen's hypnotic control waves. The Doctor tasks Zoe and Professor Watkins with constructing these devices urgently, elevating their mission to a race against time. The depolarizer becomes the linchpin of humanity's survival strategy, offering a proactive countermeasure to the Cybermen's systemic threat.

The depolarizers are the lifeline in this scene—the wearable devices designed to block the Cybermen’s hypnotic control signal. Though only three have been constructed, their existence is a fragile hope against the invasion. The Doctor’s urgency to find more neuristors is directly tied to the need to produce additional depolarizers, as each one represents a potential shield for someone in London. Their role here is both functional (as a countermeasure) and symbolic (a tangible representation of the team’s fight against the Cybermen).