Wahoo Fitness has introduced its RPM Cadence Sensor, which is just seven grams and attaches to the bicycle crank with a 3M adhesive or a sleeve. It can connect wirelessly to an IOS device via Bluetooth 4.0. Cadence can be displayed on any compatible cycling app, including Strava, Wahoo Fitness and MapMyRide. LED lights flash when sensor is connected to the iOS app.
The sensor does not need to be charged and will run on one coin cell battery for up to two years.
Wahoo Fitness Official Website
http://www.wahoofitness.com/