France's national weather service, Météo France, has filed a criminal complaint with the gendarmerie at Roissy airport after detecting suspicious temperature spikes at the Paris Charles de Gaulle (CDG) airport weather station that coincided with large payouts on the crypto-based prediction market Polymarket. The case, which has captured headlines in Le Monde, Le Figaro, and BFMTV, involves an estimated $34,000 profit from bets that appear to have exploited a single sensor vulnerability using an ordinary hair dryer.
Two Temperature Anomalies in April
According to multiple reports, two distinct incidents occurred at the CDG automated station. On April 6, around 6:30 p.m., the temperature reading jumped by approximately 4°C within 12 minutes, briefly hitting 22.5°C before dropping back to normal. On April 15, at about 9:30 p.m., under calm, overcast skies, the reading again spiked to 22°C and receded within minutes. No neighboring stations recorded similar changes, and wind direction and relative humidity remained stable during both events.
Meteorologist Paul Marquis, founder of E-Meteo Service, told Le Figaro that natural explanations were virtually impossible. “There was no change in wind direction or relative humidity, and other stations recorded nothing,” he stated. “The most plausible cause is physical interference using a heat source placed near the probe.” The CDG station is located near the airport runway perimeter and is accessible from a roadside public area, making it feasible for someone to approach unnoticed.
Polymarket Bets Aligned with Sensor Manipulation
Polymarket, one of the world's largest crypto prediction markets, uses data from that exact station to settle daily maximum temperature markets for Paris. On April 6, a low-probability bet that Paris would reach 21°C paid out approximately $14,000 to at least one bettor whose account had been created just days earlier. On April 15, a similar bet on 22°C yielded nearly $20,000. Combined, the two events netted roughly $34,000. Polymarket users flagged both incidents in real-time, with comments pointing to manipulation and potential insider trading.
In response, Polymarket switched its data source for Paris temperature markets from CDG to Paris–Le Bourget airport on April 19, effectively delinking the compromised station. The platform remains banned in France but is still accessible to some users via VPNs or other means.
Investigation and Broader Implications
Météo France confirmed it filed a complaint for “manipulation of an automated data processing system,” but declined further comment. No arrests have been made, and the suspect(s) remain unidentified. The case has resonated widely in French meteorological forums such as Infoclimat.fr, where users flagged the April 6 data as suspicious within hours. Discussion spread to X (formerly Twitter), where posts referencing a “hair dryer at Paris airport” went viral and helped drive the story into mainstream media.
This incident underscores a critical vulnerability in prediction markets that rely on single physical sensors as data oracles. When one data point can determine the outcome of a financial market, it becomes a target. The investigation is ongoing, and it may lead to broader reforms in how decentralized prediction platforms source and verify real-world data. As regulators and market operators watch closely, the “hair dryer bet” has become a cautionary tale about the intersection of physical manipulation and crypto-based wagering.