Barbed Wire

Barbed wire is a single tile deploy-able that deals damage over time to zombies that walk over it. It can only be upgraded 3 times, two on the left and once on the right. Barbed wire cannot be destroyed, and is best used in conjunction with sandbags to slow and maim zombies before they reach the exit.

Barbed wire also appears to be used on the sandbags' left path upgrade. This only deals damage to zombies that attack the sandbags however.

Left Path

 * Razor Wire - Costs $50. Increases damage.
 * Electrified Wire - Costs 300 SAS Dollars to unlock.

Right Path

 * Double Strand Wire - Costs $35. Gives more 'Staying Power'.