Garmin's Speed Sensor 2 is an updated version of their original bike speed sensor and now comes with Bluetooth as well as ANT+. It's a single unit that sits on the wheel, so there are no magnets or other bits to stick on and line up correctly: you just hook it onto the wheel and go.
It can go on the front or rear wheel. It is easier to get it onto the front wheel, but if you want to use it with a wheel-on trainer, you need to put it on the back wheel.
In my experience, it is way easier to install than the Wahoo bike speed sensor and stays in place just as well.
