Why do you want to increase sensitivity? I've found that doing so only annoys your neigbors as the alarm goes off every time a big rig drives by.
From a safety perspective, the alarm protects pretty good...and will go off if someone breaks glass. I've never been convinced that bumping someone's car is a precursor to theft.
...in my humble opinion.
<span style='color:green'>1994 325i </span>- - - 75,000 mi.
No mods - - - very happy as is!
<span style='color:green'>1995 525i </span>- - - 154,000 mi.
No squeaks or rattles... unreal!