Everything you need to know about the device can be found on the Wahoo website here- https://www.wahoofitness.com/devices/bike-sensors/wahoo-rpm-cadence-sensor
The device you will receive will not be in retail packaging and will not include instruction booklet. You can find the instruction booklet here- https://support.wahoofitness.com/hc/en-us/articles/115000336724-RPM-Cadence-Information-and-Setup