https://www.amazon.com/Wahoo-Cadence...ce+bike+sensor is what you want. They are two individual sensors that are easily swapped between bikes, shoes, wheels, whatever. They work with both Bluetooth and ANT+, and don't require magnets. ANT+ is the only protocol to use if you have multiple devices reading them, say a bike computer and a desktop, which is my setup. On the desktop there are lots of training apps that will read them, except a lot of them are paid apps. Zwift seems to be the most popular and I use it, but prefer The Sufferfest for better training routines. You will also need a USB dongle for ANT+. Just search on Amazon and these come up.

There are also cheaper versions of the sensors, but they aren't that much cheaper and I can't vouch for them.