Before leaving the vehicle, fully press the clutch pedal down, move the shift lever into R (Reverse), and firmly apply the parking brake. Once the shift lever has been placed in R (Reverse) with the clutch pedal pressed down, the ignition key can be turned to LOCK/OFF, then remove the key and release the clutch pedal.
See Manual Transmission Operation.
Chevrolet Cobalt Owners Manual. Checking Things Under the Hood
WARNING:
An electric fan under the hood can start up and
injure you even when the engine is not running.
Keep hands, clothing, and tools away from any
underhood electric fan.
WARNING:
Things that burn can get on hot engine parts and
start a fire. These include liquids like fuel, oil,
coolant ...