I'm in the process of ordering two more sets of speed/distance sensors for two of my other road bikes.

Can my Garmin Forerunner 910XT (I was a runner long before I was a biker) detect which bike I'm on based on which sensors it detects?

If it helps, each will have a different brand. One has the GSC 10, one has the Wahoo version of the GSC 10, and one will have the wahoo cadence sensor only. My HR monitor is common to all.

Yes, according to the internet, the wahoo sensors are compatible with my watch. We'll see...

I think I remember reading something like that but I can't find it.

As long as the sensors do ANT+ your watch won't know what company made them. They'll each have a unique ANT ID. In theory your 910 could use that to determine which bike you're on, but it won't. I think it uses the "sensor pool" approach which means when you go start a ride, it looks for all of the sensors it knows about and connects to whatever is available. This allows multiple GSCs but none of them are paired to a specific bike, in fact the way Garmin implemented things, a sensor pool replaces the concept of bike profiles.

What are you trying to achieve? An odometer per bike? Having Connect/Strava tag your rides with the bike you used? Different set of data screens per bike?

In terms of automatically tracking gear based on the sensor it's paired with, No. At least my 810 doesn't do this, as far as I've seen.

There's no real link of the particular sensor with a particular piece of gear, which is what Garmin considers it. It would be nice if either the unit or the online software were smart enough to figure out that you logged a ride with sensor "X" and were riding your Specialized and always ride that bike with that sensor, but that's way too complicated for Garmin to write software for.

Indeed, the bloody unit doesn't even transfer the data in the unit as to which piece of gear was used, to the upload to Connect. You have to go into Connect to edit the gear used on that workout. I suggested this to Garmin in a service call, the tech guy "thought it was a good idea". Yeah, thanks.....