This video will explore how to find the voicings used for playing altissimo notes. It will explain what happens in the mouth and how to do various overtone exercises.

Recommended books
“VOICING” An approach to the saxophone's third register: Donald Sinta
Top Tones for the Saxophone: FourOctave Rang: Siguard Rascher
Saxophone High Tones: A Systematic Approach to the Extension of the Range of All the Saxophones: Soprano, Alto, Tenor, and Baritone: Eugene Rousseau
Ted Nash's Studies in High Harmonics: For Tenor and Alto Saxophone

The scribd website has many of these books. If the book is restricted with blurred words then open the website and book with a different search engine. For example, I could not view the Ted Nash book on this site through google chrome but was able to view it through microsoft edge. I was able to view the Donald Sinta book through google chrome by right clicking on the restricted page and choosing the option of viewing the page in another tab. Here I simply opened each page in a new tab. The scribd website usually allows new viewers to view 2 books for free without joining.
The siguard Rascher book and the Eugene Rosseau book can be found online with a quick search.

Altissimo fingerings videos
Check out the following channels:
Sean Hurlburt music: lots of videos on alto sax altissimo notes
dallassax: lots of videos on alto and tenor altissimo notes
getyoursaxtogether: a video showing many altissimo fingerings
Patrick Bartley: a video showing the fingerings he uses and how he discovered them.
Most of the popular channels will have a video on altissimo fingerings.

Time chapters
00:00 Common altissimo tips
05:12 Voicings explained
09:48 trial and error method
25:12 systematic method
32:21 playalong alto sax tone scale