London’s black cabs are as iconic as red buses, rainy skies, and overpriced pints. But beneath the charm of leather seats and well-worn cockney banter, a fringe theory suggests something more insidious might be going on…

Lets set the scene: You step into a black cab on a rainy Wednesday. You’re stressed. Tense. Tired. Twenty minutes later, you’re staring out the window, oddly numb. Not peaceful, just flat. Like your thoughts are on mute.

Coincidence? Or the effect of something darker humming beneath the vinyl seats?

According to a growing number of conspiracy theorists, London’s iconic black cabs are unknowingly fitted with low-frequency emitters designed to subtly influence passenger moods—a leftover from a Cold War-era social engineering project designed to pacify the public in times of potential unrest.

Welcome to the strange, uncomfortable idea that the cab isn’t just taking you somewhere, it might be changing you on the way.

In the 1950s and 60s, psychological warfare became a formal branch of statecraft in both the UK and the US. From MK-Ultra in America (yes, very much real, and heavily documented) to the British Psychological Warfare Executive (PWE) and later the Tavistock Institute, governments invested heavily in how non-lethal influence could steer public behaviour.

One line of inquiry: infrasonic, which is extremely low frequencies, below the range of human hearing, but not human response. Studies in both the UK and USSR explored how frequencies in the 4–9Hz range could cause disorientation, fatigue, or even emotional shifts.

Now this is about to get technical so stay tuned!! In 1967, a paper presented to the UK Ministry of Defence titled ‘Acoustic Influence on Urban Cohesion’, proposed the use of mobile infrasonic generators as a way to reduce civilian agitation in public transport settings. The document lists “municipal taxis” and “London buses” as potential platforms for controlled testing. Who knew you could be one person stepping into a taxi, and slightly different whren you get out. Seems like an overwhelming idea when all you wanted was to go on a night out!! 

It’s unclear whether the tech was ever deployed at scale. But throughout the 1970s, audio surveillance and behavioural influence were being explored in various public settings. According to a 1974 MoD briefing on ‘urban compliance modulation’, low-frequency sound emitters were fitted to a small fleet of government service vehicles as part of a pilot called Project FOXTONE. The results, labelled as ‘statistically neutral but behaviourally suggestive’, were never published publicly.

NOW, LETS ENTER THE BLACK CAB !! Taxis were a logical next step. Enclosed. Intimate. Unregulated compared to buses or tubes. Beginning in the late 70s, several manufacturers began including “acoustic dampening modules” in their black cab upgrades,ostensibly to reduce engine noise. But leaked trade documents from Metrocab and LTI between 1982–1991 show components with odd identifiers: “LF Res Node,” “Resonance Field Damping,” “T-Class Filter Units.”

Some claimed they were simple audio modulators. Others whispered about hidden tech, covert psychological dampeners, especially after the 1990 Poll Tax riots, when the need for subtle emotional management in the capital reached new heights. Crazy stuff. Im almost annoyed they haven’t used this to calm people in other situations, like students the day before they hand in their dissertation. 

Is this even real though?? We don’t know. A representative of Transport for London strongly denies the presence of any active “mood-altering” devices in cabs, stating:

“We have no record of any technology that would manipulate or affect the emotional state of passengers. Claims of this nature are not supported by the vehicle specifications or maintenance records.”

“your paying for your journey, not a mind altering device too, that sounds ridiculous”. 

But gaps remain.

A 2012 acoustic study by the University of Sussex (on urban soundscapes) noted unexplained low-frequency pulses in black cab interiors at around 6.3Hz, well below the audible threshold, but well within the brain’s theta rhythm range.

Before we frenzy over whether this is true, here’s what we do know:

• Governments have studied infrasonics as tools for mass behavioural influence.
• Vehicles, including taxis, have been considered delivery platforms.
• Frequencies capable of altering brain states are real, and scientifically measurable.
• Devices capable of emitting those frequencies have been quietly integrated into city infrastructure before. (See: the “Mosquito” system, used to repel teens from loitering with high-frequency noise.)

So maybe there’s nothing in the cabs.

Or maybe there’s something, and it’s been there for a very long time.