Buckle up
Definition 1 of 2
Pro Tip 1/3Literal Meaning
Directly refers to securing the safety belt in a vehicle. 
Every time I get into the car, I buckle up.
Pro Tip 2/3Legal Requirement
Buckling up in a vehicle is often required by law for safety. 
She reminded her friend to buckle up or risk a fine.
Pro Tip 3/3Safety Emphasis
The phrase stresses the importance of safety measures in vehicles. 
The driving instructor insisted to always buckle up.