What was the circular sensor Pauline Ferrand-Prévot was wearing on her back at the Tour de France Femmes?

Pauline Ferrand-Prévot rode to victory on the final stage of the Tour de France Femmes yesterday, clinching the overall race title in the process.

The win represented the first French win in a female version of the Tour de France (which has been run on and off in various formats over the years) since Catherine Marsal’s victory in the 1990 Tour de la CEE féminin.