[Johnny got his gun]

Sentries in TFC were cool. Sentries in CS are cool.
Sentry guns are stationary engineering wonders that fire bullets at and kill your enemies.
Sentry guns can be upgraded twice, with the help of a team member, to be bigger and meaner.
You can remotely choose to detonate a specific sentry, or all of them.
You can also remotely look through the spycam mounted on your sentry.