The REP (Redstone Ether Pulse) is a wireless redstone EMP (electromagnetic pulse). It will jam wireless devices in the detonation radius. To activate the REP it needs to be thrown by a player by right-clicking while holding the REP. The REP detonates when it hits a block (such as a building wall or the ground), although it can be detonated early by right clicking again. A REP can only be thrown every 2 seconds. When throwing the REP it is possible to damage both yourself or players, in combination with a deployer, this could be used inside a trap.
It is possible to fire an REP from a Deployer. When given a pulse, the Deployer will fire the REP, and when given a second pulse shortly after the first, it will detonate the REP early. Note: When detonating early using the Deployer, there should be at least one REP left in the Deployer itself, otherwise it won't work.
Even though its primary use is for jamming wireless redstone devices, it can also cause damage and/or kill mobs or unarmored players (even the player throwing it).
The appearance of detonation is a mass of orange "tendrils". Objects or entities will only be affected if hit by these tendrils. The detonation radius is about 10 blocks. The tendrils created by the REP cannot penetrate blocks, so any devices that are fully enclosed will be impervious to the REP's effect.
It is also good for griefing purposes and can be used to disable forcefields. As a result of this, it has been banned on many servers.
Using a Deployer in SMP can crash the game. It potentially will corrupt the RedPower mod files. A possible fix to this is to delete and re-add the Redpower mod.