The axe (or fire axe) is a tool used by Fireman characters in LEGO City Undercover and LEGO City Undercover: The Chase Begins. It allows the player to break open boarded-up doors. In LEGO City Undercover, it is unlocked in Special Assignment - Hot Property shortly after the fireman disguise. In The Chase Begins, it's unlocked at the start of Always Bank on Chase.
The Minotaur, Viking and Lumberjack Civilian characters have axes which can also be used to open boarded doors.
With the Super Axe Smash Red Brick, players can smash boarded-up doors faster.