A detpak or det-pack is a device that will detonate an object it is placed on. Be careful where you stick that thing! The Decepticons began using Dark Energon detpaks after Megatron got control of the stuff. Starscream carries an EMP variant of the detpak which he enjoys stealthily attaching to unwary enemies.
Starscream, Thundercracker, and Skywarp used det-packs during their mission to reactivate the Geosynchronous Energon Bridge. They tended to be the primary way for the Decepticons to corrupt stuff with Dark Energon when Megatron wasn't doing it personally.
The Decepticons attached a detpak to the door to the Autobot City nerve center, which Optimus Prime, along with Warpath, had to carefully remove before they could enter. Vortex, Cliffjumper, and Starscream all used detpaks in their missions... the latter with a bit more enthusiasm than is considered healthy.