Rick pointed out two more options for Bb on saxophone, they’re a bit less common, but can be used when it makes sense in context.  And one of them actually brings up the idea of saxophone harmonics….

The first is using the low Bb fingering with the octave key.  You can actually use the low Bb fingering to play many more notes than just the low Bb.  The first note up is the Bb an octave higher, then comes F, then Bb, then D, etc….. keeps going up the ‘harmonic series’.  What you’re doing is using your throat to create different standing waves of air within the tube of the saxophone.  The Bb up an octave comes out easier using the octave key (but it’s not completely necessary).

The notes on a saxophone start off from the vibration of the reed and then a wave pattern is set up in the body of the saxophone.  The keys change the length and escape options for the air.  The wave pattern is not limited to the saxophone though!

You are connected to the saxophone so your throat, lungs, etc are part of the system that creates the sound and shape the waves of air.

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Another Bb fingering that is a little less in tune uses the middle finger in the right hand that’s used for F#.  It’s useful if you’re doing something like passing from Bb to F#.