Garmin's magnetless speed sensor and magnetless cadence sensor allow you to measure speed and cadence, respectively, with two simple sensors that are easy to install and easy to move from bike to bike.
The speed sensor attaches to the hub of either wheel to give you accurate speed and distance at all times, including indoors on a bike trainer. The speed sensor tucks into the speed sensor sleeve which fastens around the hub.
The cadence sensor attaches to your non-drive side crank arm and measures pedal strokes per minute. The sensor comes with three differently sized straps so that one will fit your crank arm.
Speed sensor sleeve
3 cadence sensor straps