I have an alien shapeshifter character attempting to slip past its pursuers within a roughly modern-day military installation.
The shapeshifter in question can for the most part freely alter its shape, as long as its mass doesn't change. Other than the conceit of the mechanics of the shapeshifting, the rest of the setting is meant to be grounded.
Within the setting, they are being actively surveilled by security cameras, which complicates most of the classic shapeshifter tricks. How could they possibly slip past being actively monitored in order to move about freely?