The Speed Sensor 2 fits around the hub of either wheel and reports wheel speed. There are no magnets and nothing to align against a fork or stay, which is what makes it quick to move between bikes and hard to knock out of adjustment.
Wheel size can be entered in Garmin Connect or self-calibrated by a paired Edge computer or compatible Garmin device. The sensor also records on its own and uploads the ride the next time it connects, so speed and distance are captured even on a ride where you left the computer at home.
It is the reliable way to get accurate speed indoors on a trainer or anywhere GPS is unavailable or unreliable.
