This thing -
https://www.trekbikes.com/us/en_US/equipment/cycling-components/bike-saddles/bontrager-integrated-speed-storage/p/14683/?colorCode=black
https://www.trekbikes.com/us/en_US/equipment/cycling-components/bike-saddles/bontrager-integrated-speed-storage/p/14683/?colorCode=black