Crowbar

Pries boarded doors open, and it's a fast weapon too.

The key to Boarded buildings. It's also one of the fast-swinging weapons, so it makes a good everyday weapon once you've found or made one.

Where to find it

Chance that one search turns one up. Loot gets better as you level up (in co-op, the lowest level in the group counts).

Search a	Needs	Level 1	Level 10	How common
Firetruck	Level 3+	—	18%	—
Police	Level 2+	—	5%	—
Tools	Level 2+	—	4%	—

Craft one in Bag → Craft from 2× Metal + 2× Scrap Metal (4 XP)

Notice-board jobs can pay a Crowbar once you reach level 2. See Jobs.

The infected — all of them. How many swings that takes depends on your MELEE skill, what you are wearing and what you are buffed on, so nobody can put a number on it.
A fast weapon — less damage a swing, but more swings and less stamina, which is what you want in a doorway.