Modern adaptations have applied these alignments to linebackers and safeties. As a general rule, even numbered techniques dictate that you are responsible for 2 gaps; the gaps on both sides of the offensive player you are lined up against, and are often asked not to over penetrate and instead "hold" the line. Odd numbered techniques are responsible for 1 gap, typically the gap they are lined across from, and are asked to penetrate through that gap. Some coaches apply double gap responsibilities to odd techniques though, and a prime example of this is the famous "5-technique End" we often hear about when referencing a 3-4 defense. A 5 technique End is lined up on the outside shoulder of the tackle, but in a 3-4 is responsible for both the C and B gaps. Typically this is done by forcing the Tackle to block him, thus tilting him towards him, and the angle creates an option to go to either gap.
The above table shows typically
how these alignments are used today. A 5-technique can be confusing, because typically the weak side pass rusher in a 4-3 is also aligned in a 5-technique. The 2 technique is typically reserved for 3-4 inside linebackers. Outside techniques (6,7,8,9) are typically for 3-4 linebackers and/or safeties.
It at gets a little confusing because every team, college and professional, usually has a slight adaptation to these alignments and/or responsibilities. However, this is the most general
use of the Bear Bryant system.
I hope this clears things up a bit.