We test the effectiveness of a social comparison nudge to enhance lockdown compliance during the Covid-19 pandemic, using a French representative sample (N=1154). Respondents were randomly assigned to a favourable/unfavourable informational feedback (daily road traffic mobility patterns, in Normandy - a region of France) on peer lockdown compliance. Our dependent variable was the intention to comply with a possible future lockdown. We controlled for risk, time, and social preferences and tested the effectiveness of the nudge. We found no evidence of the effectiveness of the social comparison nudge among the whole French population, but the nudge was effective when its recipient and the reference population shared the same geographical location (Normandy). Exploratory results on this subsample (N=52) suggest that this effectiveness could be driven by non-cooperative individuals.