Wahoo Blue SC Speed and Cadence Sensor
Smartphones have replaced an amazing number of single-purpose gadgets. Among them: the bike computer. Still, a smartphone needs help if it wants to get close to the utility of a purpose-built bike computer. And while GPS might be accurate enough for some, a speed sensor is even more precise. Initially, the solution was to add an ANT+ adapter to your smartphone and use one of the many sensors already available. Now, of course, we have Bluetooth Low Energy, which provides the low power consumption of ANT+ but without the need for a dongle.
The first Bluetooth LE speed and cadence sensor for bikes is the Wahoo Blue SC, which sells for a reasonable $60. The single sensor can mount to the bike's chainstay via an included rubber strap or a couple of cable ties. I went with the cable ties, as I didn't trust the strap to withstand the perils of mountain biking. The other pieces are two magnets. One mounts on a spoke, like most cycling speed sensors; the other, to the left crank arm. The sensor has an adjustable arm that's easy to adjust so that you can get it close to the spoke, but the magnet for the spoke wasn't the best I've seen. Ultimately, I ended up using one from another speed sensor. The setup is on par with other speed and cadence sensors I've seen and it stays in place. I'm also happy to say it's managed to survive the muddy summer trails, as well as the bike washes that follow. Oh, and the included coin battery lasted about six months, or 600 miles.
Of course, the Wahoo Blue SC also integrates with Wahoo's own cycling computer app, but it works with plenty of others too, like the one I use, Mountain Bike Pro. I was a bit concerned about the effects on my smartphone's battery of running Bluetooth LE all the time, but haven't noticed any degradation in battery life. Overall the Wahoo Blue SC has become essential to tracking my rides, with the only mentionable annoyance being an extra 30 seconds of prep time to test the app and the sensor.
-- Ben Drawbaugh