Pipe Bomb

The Pipe bomb is a powerful home made explosive that doubles as a diversionary device. The design is based off a stereotypical pipe bomb, but with the gutted remains of a smoke detector taped to it. It attracts any Common Infected to it (Unless they're already in melee range of a survivor) 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 as common infected will chase the pipe bomb in preference, for clearing an area of Common Infected, for conserving ammunition, and for crippling a Horde, particularly when being attacked from multiple directions.

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. There were some issues with this however: rushing infected would ignore the grenade, and often run past it, making the pipe bomb useless unless perfectly timed. Another, worse problem was when the infected not only ignored the grenade, but kicked it back toward the thrower-not in a literal sense, but it would bounce back. Valve fixed the problem by making the Pipe bomb attract Common Infected, and added the oxygen tank to perform the role of the earlier pipe bomb.

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 single-player, will not be attracted by the pipe bomb. Molotovs or gas cans are preferable in these situations.
 * In Versus Mode, the distinct beep of the pipe bomb will make then almost useless against infected players, as they can easily avoid them, or even run right past them.
 * During a finale, it is always good for at least one player to hold onto a pipe bomb until the Rescue vehicle arrives, then to use it. This will distract the Horde long enough to get in the rescue vehicle.
 * Infected who are within attacking range will not be pulled away by the pipe bomb itself. Melee them away before throwing the bomb to cause them to run off. While they may still be stunned by the melee long enough to be liquified by the blast, at the very least, they will be drawn away from you and will forget you long enough to gun them down.