Pipe Bomb

The Pipe bomb is a powerful canister-like grenade that features the customised parts of a fire alarm attached to it and emits a beeping sound when thrown. It strongly attracts Common Infected to it and detonates when its fuse is depleted, killing nearby Infected. The Pipe bomb may also damage Survivors caught in its explosion radius. The Pipe bomb is extremely handy for defending victims of the Boomer, for clearing an area of Common Infected, for conserving ammunition, and for crippling a Horde. It is much rarer than the Molotov.

According to the game's developer commentary, as it was originally conceived, the Pipe bomb did not have the flashing light; instead, it served as a conventional grenade. Because the Infected were prone to rushing at close quarters, the Pipe bomb was far less useful than the Molotov, which would kill all the Common Infected who rushed through the flames. Valve fixed the problem by making the Pipe bomb attract Common Infected.

Tactics

 * Hold on to Pipe bombs until attacked by a large Horde. The effectiveness of the Pipe bomb is proportional to the number of infected nearby.
 * If there are Common Infected who are visibly unable to reach the Pipe bomb before its detonation, shoot them as they are running so that there are less leftovers to kill. Large groups can be thinned out quickly this way. A pipe bomb can be combined with a molotov cocktail for a similar effect.
 * Throwing multiple Pipe bombs at once is inefficient, as Common Infected tend to run towards the first one thrown. Let your teammates know when you are going to throw a Pipe bomb.
 * During a Finale or panic event, throw the Pipe bomb when most of the Horde are on their feet. If a Common Infected is climbing when a Pipe bomb is thrown, then they will finish climbing before they run towards the Pipe bomb and therefore they may not reach it in time.
 * The Common Infected who are not killed by the explosion are stunned, and therefore very vulnerable to attack.
 * Note that special infected, in campaign or singleplayer, will not be attracted by the pipe bomb. Molotovs are preferable in these situations.